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	$99.34	12.369%	$111.6274	$111.63	$111.65	$111.60
Purchase #2	$57.59	13.317%	$65.2593	$65.26	$65.25	$65.30
Purchase #3	$133.51	4.294%	$139.2429	$139.24	$139.25	$139.20
Purchase #4	$85.77	4.430%	$89.5696	$89.57	$89.55	$89.60
Purchase #5	$131.41	3.866%	$136.4903	$136.49	$136.50	$136.50
Purchase #6	$247.71	10.123%	$272.7857	$272.79	$272.80	$272.80
Purchase #7	$80.72	7.716%	$86.9484	$86.95	$86.95	$86.90
7 purchase totals =	$836.05		$901.9236	$901.93	$901.95	$901.90