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	$202.33	3.242%	$208.8895	$208.89	$208.90	$208.90
Purchase #2	$31.47	4.855%	$32.9979	$33.00	$33.00	$33.00
Purchase #3	$145.74	9.242%	$159.2093	$159.21	$159.20	$159.20
Purchase #4	$163.57	6.434%	$174.0941	$174.09	$174.10	$174.10
Purchase #5	$143.33	6.640%	$152.8471	$152.85	$152.85	$152.80
Purchase #6	$92.86	8.174%	$100.4504	$100.45	$100.45	$100.50
Purchase #7	$55.32	3.266%	$57.1268	$57.13	$57.15	$57.10
7 purchase totals =	$834.62		$885.6151	$885.62	$885.65	$885.60