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	$99.89	11.718%	$111.5951	$111.60	$111.60	$111.60
Purchase #2	$244.99	10.222%	$270.0329	$270.03	$270.05	$270.00
Purchase #3	$250.51	5.601%	$264.5411	$264.54	$264.55	$264.50
Purchase #4	$145.94	3.830%	$151.5295	$151.53	$151.55	$151.50
Purchase #5	$53.73	10.624%	$59.4383	$59.44	$59.45	$59.40
Purchase #6	$121.68	11.194%	$135.3009	$135.30	$135.30	$135.30
Purchase #7	$191.92	3.873%	$199.3531	$199.35	$199.35	$199.40
7 purchase totals =	$1,108.66		$1,191.7909	$1,191.79	$1,191.85	$1,191.70