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	$100.94	3.460%	$104.4325	$104.43	$104.45	$104.40
Purchase #2	$139.79	11.814%	$156.3048	$156.30	$156.30	$156.30
Purchase #3	$136.51	13.680%	$155.1846	$155.18	$155.20	$155.20
Purchase #4	$34.59	13.188%	$39.1517	$39.15	$39.15	$39.20
Purchase #5	$175.62	8.375%	$190.3282	$190.33	$190.35	$190.30
Purchase #6	$222.63	5.459%	$234.7834	$234.78	$234.80	$234.80
Purchase #7	$130.98	8.146%	$141.6496	$141.65	$141.65	$141.60
7 purchase totals =	$941.06		$1,021.8348	$1,021.82	$1,021.90	$1,021.80