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	$34.99	5.666%	$36.9725	$36.97	$36.95	$37.00
Purchase #2	$31.69	3.456%	$32.7852	$32.79	$32.80	$32.80
Purchase #3	$238.57	7.142%	$255.6087	$255.61	$255.60	$255.60
Purchase #4	$184.53	6.464%	$196.458	$196.46	$196.45	$196.50
Purchase #5	$81.56	12.469%	$91.7297	$91.73	$91.75	$91.70
Purchase #6	$83.49	8.576%	$90.6501	$90.65	$90.65	$90.70
Purchase #7	$195.85	11.463%	$218.3003	$218.30	$218.30	$218.30
7 purchase totals =	$850.68		$922.5045	$922.51	$922.50	$922.60