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	$85.77	4.547%	$89.67	$89.67	$89.65	$89.70
Purchase #2	$131.86	10.795%	$146.0943	$146.09	$146.10	$146.10
Purchase #3	$57.89	6.628%	$61.7269	$61.73	$61.75	$61.70
Purchase #4	$105.51	9.543%	$115.5788	$115.58	$115.60	$115.60
Purchase #5	$111.54	9.643%	$122.2958	$122.30	$122.30	$122.30
Purchase #6	$83.78	10.633%	$92.6883	$92.69	$92.70	$92.70
Purchase #7	$126.47	12.370%	$142.1143	$142.11	$142.10	$142.10
7 purchase totals =	$702.82		$770.1684	$770.17	$770.20	$770.20