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	$131.55	6.701%	$140.3652	$140.37	$140.35	$140.40
Purchase #2	$234.80	8.785%	$255.4272	$255.43	$255.45	$255.40
Purchase #3	$62.70	11.517%	$69.9212	$69.92	$69.90	$69.90
Purchase #4	$57.53	3.613%	$59.6086	$59.61	$59.60	$59.60
Purchase #5	$86.75	7.733%	$93.4584	$93.46	$93.45	$93.50
Purchase #6	$230.90	4.144%	$240.4685	$240.47	$240.45	$240.50
Purchase #7	$235.98	8.862%	$256.8925	$256.89	$256.90	$256.90
7 purchase totals =	$1,040.21		$1,116.1416	$1,116.15	$1,116.10	$1,116.20