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	$134.45	13.428%	$152.5039	$152.50	$152.50	$152.50
Purchase #2	$45.49	10.340%	$50.1937	$50.19	$50.20	$50.20
Purchase #3	$197.71	4.228%	$206.0692	$206.07	$206.05	$206.10
Purchase #4	$97.26	5.782%	$102.8836	$102.88	$102.90	$102.90
Purchase #5	$130.89	13.400%	$148.4293	$148.43	$148.45	$148.40
Purchase #6	$25.87	11.437%	$28.8288	$28.83	$28.85	$28.80
Purchase #7	$140.92	6.568%	$150.1756	$150.18	$150.20	$150.20
7 purchase totals =	$772.59		$839.0841	$839.08	$839.15	$839.10