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	$40.42	4.422%	$42.2074	$42.21	$42.20	$42.20
Purchase #2	$55.31	10.467%	$61.0993	$61.10	$61.10	$61.10
Purchase #3	$97.25	3.268%	$100.4281	$100.43	$100.45	$100.40
Purchase #4	$159.61	10.748%	$176.7649	$176.76	$176.75	$176.80
Purchase #5	$223.67	8.692%	$243.1114	$243.11	$243.10	$243.10
Purchase #6	$247.69	4.560%	$258.9847	$258.98	$259.00	$259.00
Purchase #7	$189.98	4.702%	$198.9129	$198.91	$198.90	$198.90
7 purchase totals =	$1,013.93		$1,081.5087	$1,081.50	$1,081.50	$1,081.50