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	$134.64	13.668%	$153.0426	$153.04	$153.05	$153.00
Purchase #2	$13.47	8.104%	$14.5616	$14.56	$14.55	$14.60
Purchase #3	$91.45	3.618%	$94.7587	$94.76	$94.75	$94.80
Purchase #4	$55.87	9.569%	$61.2162	$61.22	$61.20	$61.20
Purchase #5	$31.87	4.448%	$33.2876	$33.29	$33.30	$33.30
Purchase #6	$42.35	6.753%	$45.2099	$45.21	$45.20	$45.20
Purchase #7	$91.79	9.460%	$100.4733	$100.47	$100.45	$100.50
7 purchase totals =	$461.44		$502.5499	$502.55	$502.50	$502.60