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	$32.56	3.591%	$33.7292	$33.73	$33.75	$33.70
Purchase #2	$95.28	4.827%	$99.8792	$99.88	$99.90	$99.90
Purchase #3	$30.37	6.581%	$32.3686	$32.37	$32.35	$32.40
Purchase #4	$158.48	10.524%	$175.1584	$175.16	$175.15	$175.20
Purchase #5	$122.68	7.166%	$131.4712	$131.47	$131.45	$131.50
Purchase #6	$219.59	9.300%	$240.0119	$240.01	$240.00	$240.00
Purchase #7	$194.73	4.708%	$203.8979	$203.90	$203.90	$203.90
7 purchase totals =	$853.69		$916.5164	$916.52	$916.50	$916.60