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	$137.87	13.797%	$156.8919	$156.89	$156.90	$156.90
Purchase #2	$90.76	13.823%	$103.3058	$103.31	$103.30	$103.30
Purchase #3	$157.71	7.175%	$169.0257	$169.03	$169.05	$169.00
Purchase #4	$202.97	10.797%	$224.8847	$224.88	$224.90	$224.90
Purchase #5	$69.72	4.622%	$72.9425	$72.94	$72.95	$72.90
Purchase #6	$54.95	8.650%	$59.7032	$59.70	$59.70	$59.70
Purchase #7	$24.25	4.207%	$25.2702	$25.27	$25.25	$25.30
7 purchase totals =	$738.23		$812.0240	$812.02	$812.05	$812.00