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	$224.77	13.473%	$255.0533	$255.05	$255.05	$255.10
Purchase #2	$96.52	8.414%	$104.6412	$104.64	$104.65	$104.60
Purchase #3	$38.65	11.570%	$43.1218	$43.12	$43.10	$43.10
Purchase #4	$133.56	7.432%	$143.4862	$143.49	$143.50	$143.50
Purchase #5	$234.47	13.191%	$265.3989	$265.40	$265.40	$265.40
Purchase #6	$76.71	7.111%	$82.1648	$82.16	$82.15	$82.20
Purchase #7	$93.82	3.315%	$96.9301	$96.93	$96.95	$96.90
7 purchase totals =	$898.50		$990.7963	$990.79	$990.80	$990.80