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	$153.45	12.615%	$172.8077	$172.81	$172.80	$172.80
Purchase #2	$208.47	4.658%	$218.1805	$218.18	$218.20	$218.20
Purchase #3	$164.35	13.426%	$186.4156	$186.42	$186.40	$186.40
Purchase #4	$240.36	6.735%	$256.5482	$256.55	$256.55	$256.50
Purchase #5	$198.79	4.726%	$208.1848	$208.18	$208.20	$208.20
Purchase #6	$65.34	3.852%	$67.8569	$67.86	$67.85	$67.90
Purchase #7	$139.40	8.352%	$151.0427	$151.04	$151.05	$151.00
7 purchase totals =	$1,170.16		$1,261.0364	$1,261.04	$1,261.05	$1,261.00