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	$203.35	6.666%	$216.9053	$216.91	$216.90	$216.90
Purchase #2	$248.29	11.529%	$276.9154	$276.92	$276.90	$276.90
Purchase #3	$97.83	13.636%	$111.1701	$111.17	$111.15	$111.20
Purchase #4	$160.59	7.637%	$172.8543	$172.85	$172.85	$172.90
Purchase #5	$152.93	10.593%	$169.1299	$169.13	$169.15	$169.10
Purchase #6	$235.59	5.330%	$248.1469	$248.15	$248.15	$248.10
Purchase #7	$36.27	13.124%	$41.0301	$41.03	$41.05	$41.00
7 purchase totals =	$1,134.85		$1,236.1520	$1,236.16	$1,236.15	$1,236.10