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	$61.94	3.532%	$64.1277	$64.13	$64.15	$64.10
Purchase #2	$127.54	13.601%	$144.8867	$144.89	$144.90	$144.90
Purchase #3	$36.75	10.651%	$40.6642	$40.66	$40.65	$40.70
Purchase #4	$240.35	10.148%	$264.7407	$264.74	$264.75	$264.70
Purchase #5	$185.61	7.398%	$199.3414	$199.34	$199.35	$199.30
Purchase #6	$114.68	8.383%	$124.2936	$124.29	$124.30	$124.30
Purchase #7	$74.46	5.307%	$78.4116	$78.41	$78.40	$78.40
7 purchase totals =	$841.33		$916.4659	$916.46	$916.50	$916.40