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	$53.48	3.539%	$55.3727	$55.37	$55.35	$55.40
Purchase #2	$98.91	10.684%	$109.4775	$109.48	$109.50	$109.50
Purchase #3	$244.53	12.287%	$274.5754	$274.58	$274.60	$274.60
Purchase #4	$160.27	11.800%	$179.1819	$179.18	$179.20	$179.20
Purchase #5	$20.47	7.195%	$21.9428	$21.94	$21.95	$21.90
Purchase #6	$234.92	7.823%	$253.2978	$253.30	$253.30	$253.30
Purchase #7	$125.57	12.871%	$141.7321	$141.73	$141.75	$141.70
7 purchase totals =	$938.15		$1,035.5802	$1,035.58	$1,035.65	$1,035.60