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	$156.77	3.238%	$161.8462	$161.85	$161.85	$161.80
Purchase #2	$165.68	9.200%	$180.9226	$180.92	$180.90	$180.90
Purchase #3	$207.86	11.699%	$232.1775	$232.18	$232.20	$232.20
Purchase #4	$76.50	7.384%	$82.1488	$82.15	$82.15	$82.10
Purchase #5	$102.39	8.482%	$111.0747	$111.07	$111.05	$111.10
Purchase #6	$90.72	10.127%	$99.9072	$99.91	$99.90	$99.90
Purchase #7	$180.88	6.775%	$193.1346	$193.13	$193.15	$193.10
7 purchase totals =	$980.80		$1,061.2116	$1,061.21	$1,061.20	$1,061.10