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	$223.33	12.310%	$250.8219	$250.82	$250.80	$250.80
Purchase #2	$19.65	11.483%	$21.9064	$21.91	$21.90	$21.90
Purchase #3	$185.97	7.448%	$199.821	$199.82	$199.80	$199.80
Purchase #4	$17.65	10.414%	$19.4881	$19.49	$19.50	$19.50
Purchase #5	$160.39	6.336%	$170.5523	$170.55	$170.55	$170.60
Purchase #6	$85.49	5.531%	$90.2185	$90.22	$90.20	$90.20
Purchase #7	$157.79	5.117%	$165.8641	$165.86	$165.85	$165.90
7 purchase totals =	$850.27		$918.6723	$918.67	$918.60	$918.70