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	$231.60	8.307%	$250.839	$250.84	$250.85	$250.80
Purchase #2	$137.79	11.558%	$153.7158	$153.72	$153.70	$153.70
Purchase #3	$228.82	13.208%	$259.0425	$259.04	$259.05	$259.00
Purchase #4	$22.89	13.642%	$26.0127	$26.01	$26.00	$26.00
Purchase #5	$128.33	12.389%	$144.2288	$144.23	$144.25	$144.20
Purchase #6	$88.66	11.811%	$99.1316	$99.13	$99.15	$99.10
Purchase #7	$70.60	3.337%	$72.9559	$72.96	$72.95	$73.00
7 purchase totals =	$908.69		$1,005.9263	$1,005.93	$1,005.95	$1,005.80