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	$92.77	12.563%	$104.4247	$104.42	$104.40	$104.40
Purchase #2	$184.46	13.404%	$209.185	$209.19	$209.20	$209.20
Purchase #3	$87.42	13.667%	$99.3677	$99.37	$99.35	$99.40
Purchase #4	$13.84	7.653%	$14.8992	$14.90	$14.90	$14.90
Purchase #5	$132.83	6.538%	$141.5144	$141.51	$141.50	$141.50
Purchase #6	$85.46	7.819%	$92.1421	$92.14	$92.15	$92.10
Purchase #7	$165.90	10.648%	$183.565	$183.57	$183.55	$183.60
7 purchase totals =	$762.68		$845.0981	$845.10	$845.05	$845.10