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	$85.36	3.366%	$88.2332	$88.23	$88.25	$88.20
Purchase #2	$63.47	6.269%	$67.4489	$67.45	$67.45	$67.40
Purchase #3	$33.45	7.177%	$35.8507	$35.85	$35.85	$35.90
Purchase #4	$138.38	10.231%	$152.5377	$152.54	$152.55	$152.50
Purchase #5	$34.83	8.279%	$37.7136	$37.71	$37.70	$37.70
Purchase #6	$185.55	10.779%	$205.5504	$205.55	$205.55	$205.60
Purchase #7	$28.97	12.104%	$32.4765	$32.48	$32.50	$32.50
7 purchase totals =	$570.01		$619.8110	$619.81	$619.85	$619.80