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	$128.65	3.281%	$132.871	$132.87	$132.85	$132.90
Purchase #2	$39.86	7.196%	$42.7283	$42.73	$42.75	$42.70
Purchase #3	$242.63	13.708%	$275.8897	$275.89	$275.90	$275.90
Purchase #4	$163.69	11.710%	$182.8581	$182.86	$182.85	$182.90
Purchase #5	$222.56	6.137%	$236.2185	$236.22	$236.20	$236.20
Purchase #6	$143.74	8.438%	$155.8688	$155.87	$155.85	$155.90
Purchase #7	$193.87	10.613%	$214.4454	$214.45	$214.45	$214.40
7 purchase totals =	$1,135.00		$1,240.8798	$1,240.89	$1,240.85	$1,240.90