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	$12.46	5.106%	$13.0962	$13.10	$13.10	$13.10
Purchase #2	$146.82	3.462%	$151.9029	$151.90	$151.90	$151.90
Purchase #3	$238.34	10.124%	$262.4695	$262.47	$262.45	$262.50
Purchase #4	$126.59	12.306%	$142.1682	$142.17	$142.15	$142.20
Purchase #5	$207.41	8.310%	$224.6458	$224.65	$224.65	$224.60
Purchase #6	$82.35	8.206%	$89.1076	$89.11	$89.10	$89.10
Purchase #7	$206.46	12.327%	$231.9103	$231.91	$231.90	$231.90
7 purchase totals =	$1,020.43		$1,115.3005	$1,115.31	$1,115.25	$1,115.30