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	$16.72	12.322%	$18.7802	$18.78	$18.80	$18.80
Purchase #2	$72.37	5.499%	$76.3496	$76.35	$76.35	$76.30
Purchase #3	$143.61	6.141%	$152.4291	$152.43	$152.45	$152.40
Purchase #4	$212.77	11.136%	$236.4641	$236.46	$236.45	$236.50
Purchase #5	$98.27	5.220%	$103.3997	$103.40	$103.40	$103.40
Purchase #6	$95.52	11.545%	$106.5478	$106.55	$106.55	$106.50
Purchase #7	$187.29	5.741%	$198.0423	$198.04	$198.05	$198.00
7 purchase totals =	$826.55		$892.0128	$892.01	$892.05	$891.90