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	$220.65	10.226%	$243.2137	$243.21	$243.20	$243.20
Purchase #2	$99.89	5.439%	$105.323	$105.32	$105.30	$105.30
Purchase #3	$124.62	10.688%	$137.9394	$137.94	$137.95	$137.90
Purchase #4	$84.38	13.485%	$95.7586	$95.76	$95.75	$95.80
Purchase #5	$95.45	5.263%	$100.4735	$100.47	$100.45	$100.50
Purchase #6	$76.54	13.400%	$86.7964	$86.80	$86.80	$86.80
Purchase #7	$220.80	3.819%	$229.2324	$229.23	$229.25	$229.20
7 purchase totals =	$922.33		$998.7370	$998.73	$998.70	$998.70