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	$34.86	11.456%	$38.8536	$38.85	$38.85	$38.90
Purchase #2	$151.64	11.791%	$169.5199	$169.52	$169.50	$169.50
Purchase #3	$37.95	3.598%	$39.3154	$39.32	$39.30	$39.30
Purchase #4	$178.93	5.784%	$189.2793	$189.28	$189.30	$189.30
Purchase #5	$195.41	10.559%	$216.0433	$216.04	$216.05	$216.00
Purchase #6	$11.63	5.707%	$12.2937	$12.29	$12.30	$12.30
Purchase #7	$159.53	12.409%	$179.3261	$179.33	$179.35	$179.30
7 purchase totals =	$769.95		$844.6313	$844.63	$844.65	$844.60