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	$107.94	12.760%	$121.7131	$121.71	$121.70	$121.70
Purchase #2	$51.78	9.830%	$56.87	$56.87	$56.85	$56.90
Purchase #3	$219.98	3.546%	$227.7805	$227.78	$227.80	$227.80
Purchase #4	$94.54	11.216%	$105.1436	$105.14	$105.15	$105.10
Purchase #5	$37.92	3.721%	$39.331	$39.33	$39.35	$39.30
Purchase #6	$103.67	7.580%	$111.5282	$111.53	$111.55	$111.50
Purchase #7	$13.59	6.525%	$14.4767	$14.48	$14.50	$14.50
7 purchase totals =	$629.42		$676.8431	$676.84	$676.90	$676.80