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	$228.42	13.731%	$259.7844	$259.78	$259.80	$259.80
Purchase #2	$76.72	3.761%	$79.6054	$79.61	$79.60	$79.60
Purchase #3	$90.53	11.448%	$100.8939	$100.89	$100.90	$100.90
Purchase #4	$52.94	12.764%	$59.6973	$59.70	$59.70	$59.70
Purchase #5	$201.90	3.361%	$208.6859	$208.69	$208.70	$208.70
Purchase #6	$37.48	7.649%	$40.3468	$40.35	$40.35	$40.30
Purchase #7	$193.75	4.248%	$201.9805	$201.98	$202.00	$202.00
7 purchase totals =	$881.74		$950.9942	$951.00	$951.05	$951.00