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	$90.49	3.431%	$93.5947	$93.59	$93.60	$93.60
Purchase #2	$40.73	10.685%	$45.082	$45.08	$45.10	$45.10
Purchase #3	$40.51	5.788%	$42.8547	$42.85	$42.85	$42.90
Purchase #4	$189.75	5.110%	$199.4462	$199.45	$199.45	$199.40
Purchase #5	$107.59	11.228%	$119.6702	$119.67	$119.65	$119.70
Purchase #6	$212.28	10.555%	$234.6862	$234.69	$234.70	$234.70
Purchase #7	$60.25	4.262%	$62.8179	$62.82	$62.80	$62.80
7 purchase totals =	$741.60		$798.1519	$798.15	$798.15	$798.20