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	$158.88	6.500%	$169.2072	$169.21	$169.20	$169.20
Purchase #2	$231.44	8.385%	$250.8462	$250.85	$250.85	$250.80
Purchase #3	$136.25	9.206%	$148.7932	$148.79	$148.80	$148.80
Purchase #4	$7.86	5.676%	$8.3061	$8.31	$8.30	$8.30
Purchase #5	$103.81	7.257%	$111.3435	$111.34	$111.35	$111.30
Purchase #6	$66.51	9.647%	$72.9262	$72.93	$72.95	$72.90
Purchase #7	$63.64	8.620%	$69.1258	$69.13	$69.15	$69.10
7 purchase totals =	$768.39		$830.5482	$830.56	$830.60	$830.40