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	$121.56	12.837%	$137.1647	$137.16	$137.15	$137.20
Purchase #2	$47.91	5.662%	$50.6227	$50.62	$50.60	$50.60
Purchase #3	$85.61	6.762%	$91.3989	$91.40	$91.40	$91.40
Purchase #4	$43.47	8.131%	$47.0045	$47.00	$47.00	$47.00
Purchase #5	$89.88	11.539%	$100.2513	$100.25	$100.25	$100.30
Purchase #6	$26.34	13.497%	$29.8951	$29.90	$29.90	$29.90
Purchase #7	$56.99	3.835%	$59.1756	$59.18	$59.20	$59.20
7 purchase totals =	$471.76		$515.5128	$515.51	$515.50	$515.60