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	$245.61	11.789%	$274.565	$274.57	$274.55	$274.60
Purchase #2	$54.77	11.452%	$61.0423	$61.04	$61.05	$61.00
Purchase #3	$73.94	12.493%	$83.1773	$83.18	$83.20	$83.20
Purchase #4	$164.48	10.425%	$181.627	$181.63	$181.65	$181.60
Purchase #5	$34.91	4.326%	$36.4202	$36.42	$36.40	$36.40
Purchase #6	$19.45	5.560%	$20.5314	$20.53	$20.55	$20.50
Purchase #7	$75.31	7.712%	$81.1179	$81.12	$81.10	$81.10
7 purchase totals =	$668.47		$738.4811	$738.49	$738.50	$738.40