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	$80.80	3.241%	$83.4187	$83.42	$83.40	$83.40
Purchase #2	$213.95	13.130%	$242.0416	$242.04	$242.05	$242.00
Purchase #3	$232.55	10.516%	$257.005	$257.01	$257.00	$257.00
Purchase #4	$15.57	6.374%	$16.5624	$16.56	$16.55	$16.60
Purchase #5	$167.50	3.209%	$172.8751	$172.88	$172.90	$172.90
Purchase #6	$150.50	7.311%	$161.5031	$161.50	$161.50	$161.50
Purchase #7	$151.40	10.648%	$167.5211	$167.52	$167.50	$167.50
7 purchase totals =	$1,012.27		$1,100.9270	$1,100.93	$1,100.90	$1,100.90