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	$29.68	10.702%	$32.8564	$32.86	$32.85	$32.90
Purchase #2	$147.51	3.833%	$153.1641	$153.16	$153.15	$153.20
Purchase #3	$31.41	4.385%	$32.7873	$32.79	$32.80	$32.80
Purchase #4	$121.39	3.708%	$125.8911	$125.89	$125.90	$125.90
Purchase #5	$164.89	12.486%	$185.4782	$185.48	$185.50	$185.50
Purchase #6	$37.51	11.542%	$41.8394	$41.84	$41.85	$41.80
Purchase #7	$86.92	9.446%	$95.1305	$95.13	$95.15	$95.10
7 purchase totals =	$619.31		$667.1470	$667.15	$667.20	$667.20