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	$134.65	13.554%	$152.9005	$152.90	$152.90	$152.90
Purchase #2	$108.48	9.862%	$119.1783	$119.18	$119.20	$119.20
Purchase #3	$57.79	3.214%	$59.6474	$59.65	$59.65	$59.60
Purchase #4	$93.56	6.410%	$99.5572	$99.56	$99.55	$99.60
Purchase #5	$141.48	12.864%	$159.68	$159.68	$159.70	$159.70
Purchase #6	$87.92	4.105%	$91.5291	$91.53	$91.55	$91.50
Purchase #7	$248.41	10.464%	$274.4036	$274.40	$274.40	$274.40
7 purchase totals =	$872.29		$956.8961	$956.90	$956.95	$956.90