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	$192.33	13.603%	$218.4926	$218.49	$218.50	$218.50
Purchase #2	$103.56	8.788%	$112.6609	$112.66	$112.65	$112.70
Purchase #3	$126.53	12.664%	$142.5538	$142.55	$142.55	$142.60
Purchase #4	$217.60	6.597%	$231.9551	$231.96	$231.95	$232.00
Purchase #5	$153.59	3.486%	$158.9441	$158.94	$158.95	$158.90
Purchase #6	$196.95	13.544%	$223.6249	$223.62	$223.60	$223.60
Purchase #7	$37.80	6.846%	$40.3878	$40.39	$40.40	$40.40
7 purchase totals =	$1,028.36		$1,128.6192	$1,128.61	$1,128.60	$1,128.70