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	$91.39	11.509%	$101.9081	$101.91	$101.90	$101.90
Purchase #2	$233.71	12.154%	$262.1151	$262.12	$262.10	$262.10
Purchase #3	$167.43	10.776%	$185.4723	$185.47	$185.45	$185.50
Purchase #4	$115.40	12.354%	$129.6565	$129.66	$129.65	$129.70
Purchase #5	$131.51	4.425%	$137.3293	$137.33	$137.35	$137.30
Purchase #6	$141.39	13.752%	$160.834	$160.83	$160.85	$160.80
Purchase #7	$18.94	13.303%	$21.4596	$21.46	$21.45	$21.50
7 purchase totals =	$899.77		$998.7749	$998.78	$998.75	$998.80