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	$121.60	8.139%	$131.497	$131.50	$131.50	$131.50
Purchase #2	$183.68	9.214%	$200.6043	$200.60	$200.60	$200.60
Purchase #3	$6.84	7.766%	$7.3712	$7.37	$7.35	$7.40
Purchase #4	$242.53	9.258%	$264.9834	$264.98	$265.00	$265.00
Purchase #5	$246.89	11.723%	$275.8329	$275.83	$275.85	$275.80
Purchase #6	$133.64	10.600%	$147.8058	$147.81	$147.80	$147.80
Purchase #7	$200.71	7.841%	$216.4477	$216.45	$216.45	$216.40
7 purchase totals =	$1,135.89		$1,244.5423	$1,244.54	$1,244.55	$1,244.50