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	$91.68	8.612%	$99.5755	$99.58	$99.60	$99.60
Purchase #2	$99.93	5.292%	$105.2183	$105.22	$105.20	$105.20
Purchase #3	$59.50	3.231%	$61.4224	$61.42	$61.40	$61.40
Purchase #4	$213.61	12.683%	$240.7022	$240.70	$240.70	$240.70
Purchase #5	$143.90	8.581%	$156.2481	$156.25	$156.25	$156.20
Purchase #6	$77.71	7.130%	$83.2507	$83.25	$83.25	$83.30
Purchase #7	$54.54	12.442%	$61.3259	$61.33	$61.35	$61.30
7 purchase totals =	$740.87		$807.7431	$807.75	$807.75	$807.70