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	$31.39	10.574%	$34.7092	$34.71	$34.70	$34.70
Purchase #2	$154.30	13.496%	$175.1243	$175.12	$175.10	$175.10
Purchase #3	$250.57	12.369%	$281.563	$281.56	$281.55	$281.60
Purchase #4	$137.95	4.225%	$143.7784	$143.78	$143.80	$143.80
Purchase #5	$27.39	5.587%	$28.9203	$28.92	$28.90	$28.90
Purchase #6	$247.76	12.860%	$279.6219	$279.62	$279.60	$279.60
Purchase #7	$7.54	4.827%	$7.904	$7.90	$7.90	$7.90
7 purchase totals =	$856.90		$951.6211	$951.61	$951.55	$951.60