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	$136.65	8.845%	$148.7367	$148.74	$148.75	$148.70
Purchase #2	$133.65	12.708%	$150.6342	$150.63	$150.65	$150.60
Purchase #3	$84.55	12.251%	$94.9082	$94.91	$94.90	$94.90
Purchase #4	$75.27	13.762%	$85.6287	$85.63	$85.65	$85.60
Purchase #5	$60.58	3.173%	$62.5022	$62.50	$62.50	$62.50
Purchase #6	$152.70	13.661%	$173.5603	$173.56	$173.55	$173.60
Purchase #7	$111.85	5.766%	$118.2993	$118.30	$118.30	$118.30
7 purchase totals =	$755.25		$834.2696	$834.27	$834.30	$834.20