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	$128.37	12.115%	$143.922	$143.92	$143.90	$143.90
Purchase #2	$88.52	12.717%	$99.7771	$99.78	$99.80	$99.80
Purchase #3	$87.51	11.408%	$97.4931	$97.49	$97.50	$97.50
Purchase #4	$168.54	10.458%	$186.1659	$186.17	$186.15	$186.20
Purchase #5	$115.47	11.302%	$128.5204	$128.52	$128.50	$128.50
Purchase #6	$146.56	8.131%	$158.4768	$158.48	$158.50	$158.50
Purchase #7	$102.50	9.142%	$111.8706	$111.87	$111.85	$111.90
7 purchase totals =	$837.47		$926.2259	$926.23	$926.20	$926.30