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	$54.61	12.561%	$61.4696	$61.47	$61.45	$61.50
Purchase #2	$141.78	11.521%	$158.1145	$158.11	$158.10	$158.10
Purchase #3	$146.54	8.560%	$159.0838	$159.08	$159.10	$159.10
Purchase #4	$153.48	13.689%	$174.4899	$174.49	$174.50	$174.50
Purchase #5	$84.38	9.245%	$92.1809	$92.18	$92.20	$92.20
Purchase #6	$83.83	5.501%	$88.4415	$88.44	$88.45	$88.40
Purchase #7	$228.50	8.321%	$247.5135	$247.51	$247.50	$247.50
7 purchase totals =	$893.12		$981.2937	$981.28	$981.30	$981.30