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	$136.29	10.707%	$150.8826	$150.88	$150.90	$150.90
Purchase #2	$55.86	7.662%	$60.14	$60.14	$60.15	$60.10
Purchase #3	$38.50	11.177%	$42.8031	$42.80	$42.80	$42.80
Purchase #4	$75.97	8.355%	$82.3173	$82.32	$82.30	$82.30
Purchase #5	$67.93	11.796%	$75.943	$75.94	$75.95	$75.90
Purchase #6	$52.36	7.555%	$56.3158	$56.32	$56.30	$56.30
Purchase #7	$87.98	13.779%	$100.1028	$100.10	$100.10	$100.10
7 purchase totals =	$514.89		$568.5046	$568.50	$568.50	$568.40