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	$123.42	4.369%	$128.8122	$128.81	$128.80	$128.80
Purchase #2	$193.81	4.861%	$203.2311	$203.23	$203.25	$203.20
Purchase #3	$142.29	6.709%	$151.8362	$151.84	$151.85	$151.80
Purchase #4	$140.42	6.518%	$149.5726	$149.57	$149.55	$149.60
Purchase #5	$246.43	7.678%	$265.3509	$265.35	$265.35	$265.40
Purchase #6	$113.43	12.273%	$127.3513	$127.35	$127.35	$127.40
Purchase #7	$33.74	11.174%	$37.5101	$37.51	$37.50	$37.50
7 purchase totals =	$993.54		$1,063.6644	$1,063.66	$1,063.65	$1,063.70