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	$40.43	4.457%	$42.232	$42.23	$42.25	$42.20
Purchase #2	$118.34	8.831%	$128.7906	$128.79	$128.80	$128.80
Purchase #3	$17.47	7.231%	$18.7333	$18.73	$18.75	$18.70
Purchase #4	$141.59	11.460%	$157.8162	$157.82	$157.80	$157.80
Purchase #5	$179.52	3.322%	$185.4837	$185.48	$185.50	$185.50
Purchase #6	$12.40	12.306%	$13.9259	$13.93	$13.95	$13.90
Purchase #7	$152.79	4.778%	$160.0903	$160.09	$160.10	$160.10
7 purchase totals =	$662.54		$707.0720	$707.07	$707.15	$707.00