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	$104.85	7.738%	$112.9633	$112.96	$112.95	$113.00
Purchase #2	$51.61	11.505%	$57.5477	$57.55	$57.55	$57.50
Purchase #3	$160.77	4.743%	$168.3953	$168.40	$168.40	$168.40
Purchase #4	$250.65	9.657%	$274.8553	$274.86	$274.85	$274.90
Purchase #5	$140.35	4.351%	$146.4566	$146.46	$146.45	$146.50
Purchase #6	$14.86	4.664%	$15.5531	$15.55	$15.55	$15.60
Purchase #7	$117.95	10.628%	$130.4857	$130.49	$130.50	$130.50
7 purchase totals =	$841.04		$906.2570	$906.27	$906.25	$906.40