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	$62.65	5.211%	$65.9147	$65.91	$65.90	$65.90
Purchase #2	$100.99	7.274%	$108.336	$108.34	$108.35	$108.30
Purchase #3	$87.46	4.289%	$91.2112	$91.21	$91.20	$91.20
Purchase #4	$13.76	4.111%	$14.3257	$14.33	$14.35	$14.30
Purchase #5	$136.87	3.108%	$141.1239	$141.12	$141.10	$141.10
Purchase #6	$118.31	8.358%	$128.1983	$128.20	$128.20	$128.20
Purchase #7	$99.53	12.286%	$111.7583	$111.76	$111.75	$111.80
7 purchase totals =	$619.57		$660.8681	$660.87	$660.85	$660.80