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	$219.44	12.411%	$246.6747	$246.67	$246.65	$246.70
Purchase #2	$121.93	12.864%	$137.6151	$137.62	$137.60	$137.60
Purchase #3	$221.38	13.199%	$250.5999	$250.60	$250.60	$250.60
Purchase #4	$39.87	3.156%	$41.1283	$41.13	$41.15	$41.10
Purchase #5	$105.35	11.429%	$117.3905	$117.39	$117.40	$117.40
Purchase #6	$134.60	9.141%	$146.9038	$146.90	$146.90	$146.90
Purchase #7	$89.39	13.145%	$101.1403	$101.14	$101.15	$101.10
7 purchase totals =	$931.96		$1,041.4526	$1,041.45	$1,041.45	$1,041.40