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	$45.33	11.118%	$50.3698	$50.37	$50.35	$50.40
Purchase #2	$209.71	6.586%	$223.5215	$223.52	$223.50	$223.50
Purchase #3	$82.42	12.202%	$92.4769	$92.48	$92.50	$92.50
Purchase #4	$39.38	7.560%	$42.3571	$42.36	$42.35	$42.40
Purchase #5	$88.91	11.485%	$99.1213	$99.12	$99.10	$99.10
Purchase #6	$240.98	7.873%	$259.9524	$259.95	$259.95	$260.00
Purchase #7	$42.42	8.821%	$46.1619	$46.16	$46.15	$46.20
7 purchase totals =	$749.15		$813.9609	$813.96	$813.90	$814.10