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	$202.36	12.819%	$228.3005	$228.30	$228.30	$228.30
Purchase #2	$241.90	13.430%	$274.3872	$274.39	$274.40	$274.40
Purchase #3	$148.67	10.707%	$164.5881	$164.59	$164.60	$164.60
Purchase #4	$89.56	4.768%	$93.8302	$93.83	$93.85	$93.80
Purchase #5	$107.74	13.379%	$122.1545	$122.15	$122.15	$122.20
Purchase #6	$115.90	9.867%	$127.3359	$127.34	$127.35	$127.30
Purchase #7	$36.67	3.226%	$37.853	$37.85	$37.85	$37.90
7 purchase totals =	$942.80		$1,048.4494	$1,048.45	$1,048.50	$1,048.50