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	$229.70	13.117%	$259.8297	$259.83	$259.85	$259.80
Purchase #2	$65.65	10.189%	$72.3391	$72.34	$72.35	$72.30
Purchase #3	$188.57	6.102%	$200.0765	$200.08	$200.10	$200.10
Purchase #4	$156.42	10.840%	$173.3759	$173.38	$173.40	$173.40
Purchase #5	$116.25	3.682%	$120.5303	$120.53	$120.55	$120.50
Purchase #6	$70.32	12.135%	$78.8533	$78.85	$78.85	$78.90
Purchase #7	$25.58	13.478%	$29.0277	$29.03	$29.05	$29.00
7 purchase totals =	$852.49		$934.0325	$934.04	$934.15	$934.00