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	$30.28	6.798%	$32.3384	$32.34	$32.35	$32.30
Purchase #2	$246.98	11.324%	$274.948	$274.95	$274.95	$274.90
Purchase #3	$149.39	12.613%	$168.2326	$168.23	$168.25	$168.20
Purchase #4	$153.68	9.548%	$168.3534	$168.35	$168.35	$168.40
Purchase #5	$43.78	7.345%	$46.9956	$47.00	$47.00	$47.00
Purchase #6	$78.70	13.748%	$89.5197	$89.52	$89.50	$89.50
Purchase #7	$59.72	10.735%	$66.1309	$66.13	$66.15	$66.10
7 purchase totals =	$762.53		$846.5186	$846.52	$846.55	$846.40