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	$122.59	11.852%	$137.1194	$137.12	$137.10	$137.10
Purchase #2	$79.67	7.820%	$85.9002	$85.90	$85.90	$85.90
Purchase #3	$210.53	5.137%	$221.3449	$221.34	$221.35	$221.30
Purchase #4	$111.55	12.321%	$125.2941	$125.29	$125.30	$125.30
Purchase #5	$48.85	9.343%	$53.4141	$53.41	$53.40	$53.40
Purchase #6	$40.82	6.729%	$43.5668	$43.57	$43.55	$43.60
Purchase #7	$8.90	4.191%	$9.273	$9.27	$9.25	$9.30
7 purchase totals =	$622.91		$675.9125	$675.90	$675.85	$675.90