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	$11.31	7.670%	$12.1775	$12.18	$12.20	$12.20
Purchase #2	$128.51	11.327%	$143.0663	$143.07	$143.05	$143.10
Purchase #3	$60.42	4.259%	$62.9933	$62.99	$63.00	$63.00
Purchase #4	$196.71	6.700%	$209.8896	$209.89	$209.90	$209.90
Purchase #5	$142.74	12.362%	$160.3855	$160.39	$160.40	$160.40
Purchase #6	$92.43	12.189%	$103.6963	$103.70	$103.70	$103.70
Purchase #7	$181.43	5.224%	$190.9079	$190.91	$190.90	$190.90
7 purchase totals =	$813.55		$883.1164	$883.13	$883.15	$883.20