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	$85.91	4.202%	$89.5199	$89.52	$89.50	$89.50
Purchase #2	$52.54	5.138%	$55.2395	$55.24	$55.25	$55.20
Purchase #3	$36.92	10.259%	$40.7076	$40.71	$40.70	$40.70
Purchase #4	$10.27	4.235%	$10.7049	$10.70	$10.70	$10.70
Purchase #5	$236.26	7.474%	$253.9181	$253.92	$253.90	$253.90
Purchase #6	$159.48	7.568%	$171.5494	$171.55	$171.55	$171.50
Purchase #7	$91.25	7.318%	$97.9277	$97.93	$97.95	$97.90
7 purchase totals =	$672.63		$719.5671	$719.57	$719.55	$719.40