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	$122.86	11.406%	$136.8734	$136.87	$136.85	$136.90
Purchase #2	$71.38	9.874%	$78.4281	$78.43	$78.45	$78.40
Purchase #3	$86.63	7.580%	$93.1966	$93.20	$93.20	$93.20
Purchase #4	$114.25	13.821%	$130.0405	$130.04	$130.05	$130.00
Purchase #5	$155.64	8.869%	$169.4437	$169.44	$169.45	$169.40
Purchase #6	$39.38	8.727%	$42.8167	$42.82	$42.80	$42.80
Purchase #7	$19.65	4.443%	$20.523	$20.52	$20.50	$20.50
7 purchase totals =	$609.79		$671.3220	$671.32	$671.30	$671.20