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	$90.67	9.703%	$99.4677	$99.47	$99.45	$99.50
Purchase #2	$122.57	12.465%	$137.8484	$137.85	$137.85	$137.80
Purchase #3	$89.55	12.197%	$100.4724	$100.47	$100.45	$100.50
Purchase #4	$137.98	12.179%	$154.7846	$154.78	$154.80	$154.80
Purchase #5	$92.47	8.713%	$100.5269	$100.53	$100.55	$100.50
Purchase #6	$168.48	10.282%	$185.8031	$185.80	$185.80	$185.80
Purchase #7	$168.32	7.495%	$180.9356	$180.94	$180.95	$180.90
7 purchase totals =	$870.04		$959.8387	$959.84	$959.85	$959.80