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	$24.71	9.874%	$27.1499	$27.15	$27.15	$27.10
Purchase #2	$207.59	13.317%	$235.2348	$235.23	$235.25	$235.20
Purchase #3	$137.65	7.112%	$147.4397	$147.44	$147.45	$147.40
Purchase #4	$211.33	6.527%	$225.1235	$225.12	$225.10	$225.10
Purchase #5	$110.57	11.653%	$123.4547	$123.45	$123.45	$123.50
Purchase #6	$29.53	5.826%	$31.2504	$31.25	$31.25	$31.30
Purchase #7	$213.32	13.523%	$242.1673	$242.17	$242.15	$242.20
7 purchase totals =	$934.70		$1,031.8203	$1,031.81	$1,031.80	$1,031.80