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	$185.79	13.284%	$210.4703	$210.47	$210.45	$210.50
Purchase #2	$16.79	12.504%	$18.8894	$18.89	$18.90	$18.90
Purchase #3	$137.27	7.412%	$147.4445	$147.44	$147.45	$147.40
Purchase #4	$231.48	9.681%	$253.8896	$253.89	$253.90	$253.90
Purchase #5	$137.46	10.428%	$151.7943	$151.79	$151.80	$151.80
Purchase #6	$140.45	12.490%	$157.9922	$157.99	$158.00	$158.00
Purchase #7	$34.53	10.542%	$38.1702	$38.17	$38.15	$38.20
7 purchase totals =	$883.77		$978.6505	$978.64	$978.65	$978.70