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	$90.94	9.854%	$99.9012	$99.90	$99.90	$99.90
Purchase #2	$26.84	5.105%	$28.2102	$28.21	$28.20	$28.20
Purchase #3	$61.37	5.300%	$64.6226	$64.62	$64.60	$64.60
Purchase #4	$175.80	13.513%	$199.5559	$199.56	$199.55	$199.60
Purchase #5	$244.30	13.109%	$276.3253	$276.33	$276.35	$276.30
Purchase #6	$114.76	3.244%	$118.4828	$118.48	$118.50	$118.50
Purchase #7	$154.81	7.373%	$166.2241	$166.22	$166.20	$166.20
7 purchase totals =	$868.82		$953.3221	$953.32	$953.30	$953.30