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	$12.27	3.395%	$12.6866	$12.69	$12.70	$12.70
Purchase #2	$136.56	4.315%	$142.4526	$142.45	$142.45	$142.50
Purchase #3	$242.69	10.811%	$268.9272	$268.93	$268.95	$268.90
Purchase #4	$32.39	11.795%	$36.2104	$36.21	$36.20	$36.20
Purchase #5	$64.88	12.344%	$72.8888	$72.89	$72.90	$72.90
Purchase #6	$241.51	13.104%	$273.1575	$273.16	$273.15	$273.20
Purchase #7	$136.72	6.167%	$145.1515	$145.15	$145.15	$145.20
7 purchase totals =	$867.02		$951.4746	$951.48	$951.50	$951.60