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	$195.29	13.723%	$222.0896	$222.09	$222.10	$222.10
Purchase #2	$43.54	5.289%	$45.8428	$45.84	$45.85	$45.80
Purchase #3	$217.58	3.406%	$224.9908	$224.99	$225.00	$225.00
Purchase #4	$94.96	5.518%	$100.1999	$100.20	$100.20	$100.20
Purchase #5	$184.85	13.336%	$209.5016	$209.50	$209.50	$209.50
Purchase #6	$55.45	4.369%	$57.8726	$57.87	$57.85	$57.90
Purchase #7	$44.85	7.760%	$48.3304	$48.33	$48.35	$48.30
7 purchase totals =	$836.52		$908.8277	$908.82	$908.85	$908.80