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	$234.84	8.626%	$255.0973	$255.10	$255.10	$255.10
Purchase #2	$217.49	3.657%	$225.4436	$225.44	$225.45	$225.40
Purchase #3	$199.92	9.531%	$218.9744	$218.97	$218.95	$219.00
Purchase #4	$72.37	5.612%	$76.4314	$76.43	$76.45	$76.40
Purchase #5	$35.41	5.477%	$37.3494	$37.35	$37.35	$37.30
Purchase #6	$195.81	10.622%	$216.6089	$216.61	$216.60	$216.60
Purchase #7	$35.49	3.120%	$36.5973	$36.60	$36.60	$36.60
7 purchase totals =	$991.33		$1,066.5023	$1,066.50	$1,066.50	$1,066.40