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	$5.28	7.794%	$5.6915	$5.69	$5.70	$5.70
Purchase #2	$223.77	8.253%	$242.2377	$242.24	$242.25	$242.20
Purchase #3	$50.37	10.529%	$55.6735	$55.67	$55.65	$55.70
Purchase #4	$75.47	13.104%	$85.3596	$85.36	$85.35	$85.40
Purchase #5	$123.90	3.749%	$128.545	$128.55	$128.55	$128.50
Purchase #6	$142.43	6.437%	$151.5982	$151.60	$151.60	$151.60
Purchase #7	$88.38	4.157%	$92.054	$92.05	$92.05	$92.10
7 purchase totals =	$709.60		$761.1595	$761.16	$761.15	$761.20