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	$125.46	8.787%	$136.4842	$136.48	$136.50	$136.50
Purchase #2	$237.90	11.329%	$264.8517	$264.85	$264.85	$264.90
Purchase #3	$60.80	9.208%	$66.3985	$66.40	$66.40	$66.40
Purchase #4	$32.62	3.636%	$33.8061	$33.81	$33.80	$33.80
Purchase #5	$127.41	10.504%	$140.7931	$140.79	$140.80	$140.80
Purchase #6	$82.45	8.848%	$89.7452	$89.75	$89.75	$89.70
Purchase #7	$208.70	10.370%	$230.3422	$230.34	$230.35	$230.30
7 purchase totals =	$875.34		$962.4210	$962.42	$962.45	$962.40