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	$249.95	11.767%	$279.3616	$279.36	$279.35	$279.40
Purchase #2	$27.84	13.384%	$31.5661	$31.57	$31.55	$31.60
Purchase #3	$210.53	6.598%	$224.4208	$224.42	$224.40	$224.40
Purchase #4	$32.82	13.189%	$37.1486	$37.15	$37.15	$37.10
Purchase #5	$40.83	4.239%	$42.5608	$42.56	$42.55	$42.60
Purchase #6	$61.79	8.642%	$67.1299	$67.13	$67.15	$67.10
Purchase #7	$72.75	13.459%	$82.5414	$82.54	$82.55	$82.50
7 purchase totals =	$696.51		$764.7292	$764.73	$764.70	$764.70