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	$146.28	13.203%	$165.5933	$165.59	$165.60	$165.60
Purchase #2	$59.25	3.331%	$61.2236	$61.22	$61.20	$61.20
Purchase #3	$204.92	8.428%	$222.1907	$222.19	$222.20	$222.20
Purchase #4	$104.29	4.344%	$108.8204	$108.82	$108.80	$108.80
Purchase #5	$187.72	8.796%	$204.2319	$204.23	$204.25	$204.20
Purchase #6	$222.50	8.747%	$241.9621	$241.96	$241.95	$242.00
Purchase #7	$141.70	13.205%	$160.4115	$160.41	$160.40	$160.40
7 purchase totals =	$1,066.66		$1,164.4335	$1,164.42	$1,164.40	$1,164.40