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	$66.96	3.736%	$69.4616	$69.46	$69.45	$69.50
Purchase #2	$41.86	7.855%	$45.1481	$45.15	$45.15	$45.10
Purchase #3	$25.89	9.462%	$28.3397	$28.34	$28.35	$28.30
Purchase #4	$65.82	13.687%	$74.8288	$74.83	$74.85	$74.80
Purchase #5	$176.90	10.728%	$195.8778	$195.88	$195.90	$195.90
Purchase #6	$210.85	12.747%	$237.727	$237.73	$237.75	$237.70
Purchase #7	$54.54	8.463%	$59.1557	$59.16	$59.15	$59.20
7 purchase totals =	$642.82		$710.5387	$710.55	$710.60	$710.50