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	$78.53	4.620%	$82.1581	$82.16	$82.15	$82.20
Purchase #2	$178.46	11.579%	$199.1239	$199.12	$199.10	$199.10
Purchase #3	$33.56	9.548%	$36.7643	$36.76	$36.75	$36.80
Purchase #4	$97.79	7.857%	$105.4734	$105.47	$105.45	$105.50
Purchase #5	$126.79	10.505%	$140.1093	$140.11	$140.10	$140.10
Purchase #6	$10.32	9.497%	$11.3001	$11.30	$11.30	$11.30
Purchase #7	$57.85	6.449%	$61.5807	$61.58	$61.60	$61.60
7 purchase totals =	$583.30		$636.5098	$636.50	$636.45	$636.60