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	$54.91	8.596%	$59.6301	$59.63	$59.65	$59.60
Purchase #2	$203.31	6.595%	$216.7183	$216.72	$216.70	$216.70
Purchase #3	$68.62	5.161%	$72.1615	$72.16	$72.15	$72.20
Purchase #4	$70.33	9.559%	$77.0528	$77.05	$77.05	$77.10
Purchase #5	$204.50	11.407%	$227.8273	$227.83	$227.85	$227.80
Purchase #6	$140.69	10.805%	$155.8916	$155.89	$155.90	$155.90
Purchase #7	$28.29	10.340%	$31.2152	$31.22	$31.20	$31.20
7 purchase totals =	$770.65		$840.4968	$840.50	$840.50	$840.50