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	$240.47	9.817%	$264.0769	$264.08	$264.10	$264.10
Purchase #2	$178.63	7.359%	$191.7754	$191.78	$191.80	$191.80
Purchase #3	$247.72	11.485%	$276.1706	$276.17	$276.15	$276.20
Purchase #4	$118.85	3.690%	$123.2356	$123.24	$123.25	$123.20
Purchase #5	$156.50	12.592%	$176.2065	$176.21	$176.20	$176.20
Purchase #6	$64.59	12.229%	$72.4887	$72.49	$72.50	$72.50
Purchase #7	$25.27	13.126%	$28.5869	$28.59	$28.60	$28.60
7 purchase totals =	$1,032.03		$1,132.5406	$1,132.56	$1,132.60	$1,132.60