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	$90.88	3.559%	$94.1144	$94.11	$94.10	$94.10
Purchase #2	$135.76	5.503%	$143.2309	$143.23	$143.25	$143.20
Purchase #3	$127.53	12.759%	$143.8016	$143.80	$143.80	$143.80
Purchase #4	$206.26	12.240%	$231.5062	$231.51	$231.50	$231.50
Purchase #5	$200.50	10.653%	$221.8593	$221.86	$221.85	$221.90
Purchase #6	$108.95	12.422%	$122.4838	$122.48	$122.50	$122.50
Purchase #7	$18.63	13.636%	$21.1704	$21.17	$21.15	$21.20
7 purchase totals =	$888.51		$978.1666	$978.16	$978.15	$978.20