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	$115.63	11.117%	$128.4846	$128.48	$128.50	$128.50
Purchase #2	$230.58	6.802%	$246.2641	$246.26	$246.25	$246.30
Purchase #3	$37.96	7.288%	$40.7265	$40.73	$40.75	$40.70
Purchase #4	$108.31	5.758%	$114.5465	$114.55	$114.55	$114.50
Purchase #5	$216.72	3.610%	$224.5436	$224.54	$224.55	$224.50
Purchase #6	$9.73	4.434%	$10.1614	$10.16	$10.15	$10.20
Purchase #7	$54.69	11.814%	$61.1511	$61.15	$61.15	$61.20
7 purchase totals =	$773.62		$825.8778	$825.87	$825.90	$825.90