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	$222.87	10.149%	$245.4891	$245.49	$245.50	$245.50
Purchase #2	$131.45	12.499%	$147.8799	$147.88	$147.90	$147.90
Purchase #3	$87.83	13.507%	$99.6932	$99.69	$99.70	$99.70
Purchase #4	$82.78	11.130%	$91.9934	$91.99	$92.00	$92.00
Purchase #5	$52.80	5.170%	$55.5298	$55.53	$55.55	$55.50
Purchase #6	$67.25	6.823%	$71.8385	$71.84	$71.85	$71.80
Purchase #7	$130.25	12.574%	$146.6276	$146.63	$146.65	$146.60
7 purchase totals =	$775.23		$859.0515	$859.05	$859.15	$859.00