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	$235.43	12.250%	$264.2702	$264.27	$264.25	$264.30
Purchase #2	$232.29	10.228%	$256.0486	$256.05	$256.05	$256.00
Purchase #3	$78.56	10.612%	$86.8968	$86.90	$86.90	$86.90
Purchase #4	$140.94	13.152%	$159.4764	$159.48	$159.50	$159.50
Purchase #5	$93.99	13.682%	$106.8497	$106.85	$106.85	$106.80
Purchase #6	$146.87	13.352%	$166.4801	$166.48	$166.50	$166.50
Purchase #7	$120.97	6.406%	$128.7193	$128.72	$128.70	$128.70
7 purchase totals =	$1,049.05		$1,168.7411	$1,168.75	$1,168.75	$1,168.70