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	$29.70	8.623%	$32.261	$32.26	$32.25	$32.30
Purchase #2	$152.67	11.802%	$170.6881	$170.69	$170.70	$170.70
Purchase #3	$144.73	8.175%	$156.5617	$156.56	$156.55	$156.60
Purchase #4	$231.71	10.458%	$255.9422	$255.94	$255.95	$255.90
Purchase #5	$141.73	11.569%	$158.1267	$158.13	$158.15	$158.10
Purchase #6	$146.53	6.745%	$156.4134	$156.41	$156.40	$156.40
Purchase #7	$28.85	10.291%	$31.819	$31.82	$31.80	$31.80
7 purchase totals =	$875.92		$961.8121	$961.81	$961.80	$961.80