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	$175.85	6.258%	$186.8547	$186.85	$186.85	$186.90
Purchase #2	$158.53	11.373%	$176.5596	$176.56	$176.55	$176.60
Purchase #3	$124.51	13.678%	$141.5405	$141.54	$141.55	$141.50
Purchase #4	$83.40	10.274%	$91.9685	$91.97	$91.95	$92.00
Purchase #5	$238.74	8.234%	$258.3979	$258.40	$258.40	$258.40
Purchase #6	$57.42	7.873%	$61.9407	$61.94	$61.95	$61.90
Purchase #7	$55.48	7.590%	$59.6909	$59.69	$59.70	$59.70
7 purchase totals =	$893.93		$976.9528	$976.95	$976.95	$977.00