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	$110.85	11.341%	$123.4215	$123.42	$123.40	$123.40
Purchase #2	$32.85	10.801%	$36.3981	$36.40	$36.40	$36.40
Purchase #3	$136.30	10.182%	$150.1781	$150.18	$150.20	$150.20
Purchase #4	$114.33	10.285%	$126.0888	$126.09	$126.10	$126.10
Purchase #5	$78.61	13.377%	$89.1257	$89.13	$89.15	$89.10
Purchase #6	$130.37	5.629%	$137.7085	$137.71	$137.70	$137.70
Purchase #7	$134.30	10.785%	$148.7843	$148.78	$148.80	$148.80
7 purchase totals =	$737.61		$811.7050	$811.71	$811.75	$811.70