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	$48.49	4.648%	$50.7438	$50.74	$50.75	$50.70
Purchase #2	$100.88	4.118%	$105.0342	$105.03	$105.05	$105.00
Purchase #3	$128.76	9.136%	$140.5235	$140.52	$140.50	$140.50
Purchase #4	$216.78	3.547%	$224.4692	$224.47	$224.45	$224.50
Purchase #5	$64.69	12.113%	$72.5259	$72.53	$72.55	$72.50
Purchase #6	$185.73	9.460%	$203.3001	$203.30	$203.30	$203.30
Purchase #7	$125.72	4.694%	$131.6213	$131.62	$131.60	$131.60
7 purchase totals =	$871.05		$928.2180	$928.21	$928.20	$928.10