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	$229.35	11.844%	$256.5142	$256.51	$256.50	$256.50
Purchase #2	$36.42	10.305%	$40.1731	$40.17	$40.15	$40.20
Purchase #3	$166.52	11.476%	$185.6298	$185.63	$185.65	$185.60
Purchase #4	$130.76	11.254%	$145.4757	$145.48	$145.50	$145.50
Purchase #5	$75.29	9.671%	$82.5713	$82.57	$82.55	$82.60
Purchase #6	$50.74	9.298%	$55.4578	$55.46	$55.45	$55.50
Purchase #7	$169.71	13.192%	$192.0981	$192.10	$192.10	$192.10
7 purchase totals =	$858.79		$957.9200	$957.92	$957.90	$958.00