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	$67.90	7.366%	$72.9015	$72.90	$72.90	$72.90
Purchase #2	$168.58	11.377%	$187.7593	$187.76	$187.75	$187.80
Purchase #3	$242.57	8.187%	$262.4292	$262.43	$262.45	$262.40
Purchase #4	$87.85	3.390%	$90.8281	$90.83	$90.85	$90.80
Purchase #5	$15.80	9.666%	$17.3272	$17.33	$17.35	$17.30
Purchase #6	$15.41	13.785%	$17.5343	$17.53	$17.55	$17.50
Purchase #7	$203.49	9.433%	$222.6852	$222.69	$222.70	$222.70
7 purchase totals =	$801.60		$871.4648	$871.47	$871.55	$871.40