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	$121.82	7.699%	$131.1989	$131.20	$131.20	$131.20
Purchase #2	$37.80	12.550%	$42.5439	$42.54	$42.55	$42.50
Purchase #3	$212.53	13.364%	$240.9325	$240.93	$240.95	$240.90
Purchase #4	$64.39	5.346%	$67.8323	$67.83	$67.85	$67.80
Purchase #5	$222.42	3.861%	$231.0076	$231.01	$231.00	$231.00
Purchase #6	$62.45	8.321%	$67.6465	$67.65	$67.65	$67.60
Purchase #7	$94.25	6.236%	$100.1274	$100.13	$100.15	$100.10
7 purchase totals =	$815.66		$881.2891	$881.29	$881.35	$881.10