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	$31.89	4.323%	$33.2686	$33.27	$33.25	$33.30
Purchase #2	$114.37	13.248%	$129.5217	$129.52	$129.50	$129.50
Purchase #3	$231.77	9.248%	$253.2041	$253.20	$253.20	$253.20
Purchase #4	$122.83	11.151%	$136.5268	$136.53	$136.55	$136.50
Purchase #5	$222.45	8.549%	$241.4673	$241.47	$241.45	$241.50
Purchase #6	$62.87	10.244%	$69.3104	$69.31	$69.30	$69.30
Purchase #7	$92.67	8.497%	$100.5442	$100.54	$100.55	$100.50
7 purchase totals =	$878.85		$963.8431	$963.84	$963.80	$963.80