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	$18.82	8.424%	$20.4054	$20.41	$20.40	$20.40
Purchase #2	$242.60	13.697%	$275.8289	$275.83	$275.85	$275.80
Purchase #3	$246.87	13.761%	$280.8418	$280.84	$280.85	$280.80
Purchase #4	$71.71	10.816%	$79.4662	$79.47	$79.45	$79.50
Purchase #5	$12.67	9.612%	$13.8878	$13.89	$13.90	$13.90
Purchase #6	$138.30	11.623%	$154.3746	$154.37	$154.35	$154.40
Purchase #7	$179.86	7.163%	$192.7434	$192.74	$192.75	$192.70
7 purchase totals =	$910.83		$1,017.5481	$1,017.55	$1,017.55	$1,017.50