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	$230.28	12.855%	$259.8825	$259.88	$259.90	$259.90
Purchase #2	$192.29	5.430%	$202.7313	$202.73	$202.75	$202.70
Purchase #3	$140.27	3.328%	$144.9382	$144.94	$144.95	$144.90
Purchase #4	$125.74	11.250%	$139.8858	$139.89	$139.90	$139.90
Purchase #5	$52.35	7.863%	$56.4663	$56.47	$56.45	$56.50
Purchase #6	$147.73	5.263%	$155.505	$155.51	$155.50	$155.50
Purchase #7	$77.81	6.427%	$82.8108	$82.81	$82.80	$82.80
7 purchase totals =	$966.47		$1,042.2199	$1,042.23	$1,042.25	$1,042.20