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	$217.48	9.388%	$237.897	$237.90	$237.90	$237.90
Purchase #2	$144.54	5.727%	$152.8178	$152.82	$152.80	$152.80
Purchase #3	$199.74	8.379%	$216.4762	$216.48	$216.50	$216.50
Purchase #4	$244.36	12.492%	$274.8855	$274.89	$274.90	$274.90
Purchase #5	$156.95	8.490%	$170.2751	$170.28	$170.30	$170.30
Purchase #6	$82.45	7.250%	$88.4276	$88.43	$88.45	$88.40
Purchase #7	$250.72	10.322%	$276.5993	$276.60	$276.60	$276.60
7 purchase totals =	$1,296.24		$1,417.3785	$1,417.40	$1,417.45	$1,417.40