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	$189.52	13.289%	$214.7053	$214.71	$214.70	$214.70
Purchase #2	$38.53	11.145%	$42.8242	$42.82	$42.80	$42.80
Purchase #3	$209.55	11.514%	$233.6776	$233.68	$233.70	$233.70
Purchase #4	$164.28	10.484%	$181.5031	$181.50	$181.50	$181.50
Purchase #5	$101.61	9.480%	$111.2426	$111.24	$111.25	$111.20
Purchase #6	$139.99	10.463%	$154.6372	$154.64	$154.65	$154.60
Purchase #7	$32.50	10.557%	$35.931	$35.93	$35.95	$35.90
7 purchase totals =	$875.98		$974.5210	$974.52	$974.55	$974.40