Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$24.51	9.644%	$26.8737	$26.87	$26.85	$26.90
Purchase #2	$143.69	4.801%	$150.5886	$150.59	$150.60	$150.60
Purchase #3	$227.69	7.407%	$244.555	$244.56	$244.55	$244.60
Purchase #4	$177.86	6.519%	$189.4547	$189.45	$189.45	$189.50
Purchase #5	$37.91	5.843%	$40.1251	$40.13	$40.15	$40.10
Purchase #6	$220.27	13.354%	$249.6849	$249.68	$249.70	$249.70
Purchase #7	$105.36	4.253%	$109.841	$109.84	$109.85	$109.80
7 purchase totals =	$937.29		$1,011.1230	$1,011.12	$1,011.15	$1,011.20