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	$107.49	5.167%	$113.044	$113.04	$113.05	$113.00
Purchase #2	$127.37	10.253%	$140.4292	$140.43	$140.45	$140.40
Purchase #3	$50.76	10.183%	$55.9289	$55.93	$55.95	$55.90
Purchase #4	$216.57	10.505%	$239.3207	$239.32	$239.30	$239.30
Purchase #5	$41.82	9.570%	$45.8222	$45.82	$45.80	$45.80
Purchase #6	$231.47	10.415%	$255.5776	$255.58	$255.60	$255.60
Purchase #7	$100.38	11.425%	$111.8484	$111.85	$111.85	$111.80
7 purchase totals =	$875.86		$961.9710	$961.97	$962.00	$961.80