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	$139.39	13.242%	$157.848	$157.85	$157.85	$157.80
Purchase #2	$247.58	5.289%	$260.6745	$260.67	$260.65	$260.70
Purchase #3	$30.42	13.683%	$34.5824	$34.58	$34.60	$34.60
Purchase #4	$86.77	5.815%	$91.8157	$91.82	$91.80	$91.80
Purchase #5	$176.56	9.150%	$192.7152	$192.72	$192.70	$192.70
Purchase #6	$136.97	11.630%	$152.8996	$152.90	$152.90	$152.90
Purchase #7	$176.55	11.229%	$196.3748	$196.37	$196.35	$196.40
7 purchase totals =	$994.24		$1,086.9102	$1,086.91	$1,086.85	$1,086.90