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	$249.62	6.408%	$265.6156	$265.62	$265.60	$265.60
Purchase #2	$21.60	12.865%	$24.3788	$24.38	$24.40	$24.40
Purchase #3	$78.85	7.113%	$84.4586	$84.46	$84.45	$84.50
Purchase #4	$38.98	9.602%	$42.7229	$42.72	$42.70	$42.70
Purchase #5	$169.77	7.591%	$182.6572	$182.66	$182.65	$182.70
Purchase #6	$79.60	12.380%	$89.4545	$89.45	$89.45	$89.50
Purchase #7	$120.40	6.106%	$127.7516	$127.75	$127.75	$127.80
7 purchase totals =	$758.82		$817.0392	$817.04	$817.00	$817.20