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	$141.30	5.310%	$148.803	$148.80	$148.80	$148.80
Purchase #2	$234.74	10.731%	$259.9299	$259.93	$259.95	$259.90
Purchase #3	$54.78	11.325%	$60.9838	$60.98	$61.00	$61.00
Purchase #4	$22.34	10.834%	$24.7603	$24.76	$24.75	$24.80
Purchase #5	$182.53	7.467%	$196.1595	$196.16	$196.15	$196.20
Purchase #6	$145.86	9.625%	$159.899	$159.90	$159.90	$159.90
Purchase #7	$78.35	3.589%	$81.162	$81.16	$81.15	$81.20
7 purchase totals =	$859.90		$931.6975	$931.69	$931.70	$931.80