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	$19.87	3.205%	$20.5068	$20.51	$20.50	$20.50
Purchase #2	$233.34	13.266%	$264.2949	$264.29	$264.30	$264.30
Purchase #3	$199.73	11.164%	$222.0279	$222.03	$222.05	$222.00
Purchase #4	$210.61	6.562%	$224.4302	$224.43	$224.45	$224.40
Purchase #5	$146.30	3.861%	$151.9486	$151.95	$151.95	$151.90
Purchase #6	$158.38	6.296%	$168.3516	$168.35	$168.35	$168.40
Purchase #7	$75.62	5.644%	$79.888	$79.89	$79.90	$79.90
7 purchase totals =	$1,043.85		$1,131.4480	$1,131.45	$1,131.50	$1,131.40