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	$35.90	3.510%	$37.1601	$37.16	$37.15	$37.20
Purchase #2	$116.62	10.519%	$128.8873	$128.89	$128.90	$128.90
Purchase #3	$84.96	6.499%	$90.4816	$90.48	$90.50	$90.50
Purchase #4	$176.89	7.657%	$190.4345	$190.43	$190.45	$190.40
Purchase #5	$89.25	9.493%	$97.7225	$97.72	$97.70	$97.70
Purchase #6	$228.97	6.433%	$243.6996	$243.70	$243.70	$243.70
Purchase #7	$212.37	6.121%	$225.3692	$225.37	$225.35	$225.40
7 purchase totals =	$944.96		$1,013.7548	$1,013.75	$1,013.75	$1,013.80