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	$180.73	5.413%	$190.5129	$190.51	$190.50	$190.50
Purchase #2	$86.93	5.534%	$91.7407	$91.74	$91.75	$91.70
Purchase #3	$32.34	8.730%	$35.1633	$35.16	$35.15	$35.20
Purchase #4	$71.67	9.523%	$78.4951	$78.50	$78.50	$78.50
Purchase #5	$52.34	6.539%	$55.7625	$55.76	$55.75	$55.80
Purchase #6	$60.60	12.520%	$68.1871	$68.19	$68.20	$68.20
Purchase #7	$50.29	13.603%	$57.1309	$57.13	$57.15	$57.10
7 purchase totals =	$534.90		$576.9925	$576.99	$577.00	$577.00