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	$121.62	12.740%	$137.1144	$137.11	$137.10	$137.10
Purchase #2	$183.32	11.715%	$204.7959	$204.80	$204.80	$204.80
Purchase #3	$105.52	12.209%	$118.4029	$118.40	$118.40	$118.40
Purchase #4	$56.53	9.448%	$61.871	$61.87	$61.85	$61.90
Purchase #5	$37.78	12.269%	$42.4152	$42.42	$42.40	$42.40
Purchase #6	$179.50	5.134%	$188.7155	$188.72	$188.70	$188.70
Purchase #7	$11.88	9.688%	$13.0309	$13.03	$13.05	$13.00
7 purchase totals =	$696.15		$766.3458	$766.35	$766.30	$766.30