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	$52.74	5.634%	$55.7114	$55.71	$55.70	$55.70
Purchase #2	$60.46	10.469%	$66.7896	$66.79	$66.80	$66.80
Purchase #3	$182.66	11.140%	$203.0083	$203.01	$203.00	$203.00
Purchase #4	$75.98	9.700%	$83.3501	$83.35	$83.35	$83.40
Purchase #5	$58.45	13.158%	$66.1409	$66.14	$66.15	$66.10
Purchase #6	$140.96	7.658%	$151.7547	$151.75	$151.75	$151.80
Purchase #7	$102.34	8.590%	$111.131	$111.13	$111.15	$111.10
7 purchase totals =	$673.59		$737.8860	$737.88	$737.90	$737.90