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	$130.65	12.114%	$146.4769	$146.48	$146.50	$146.50
Purchase #2	$161.51	10.716%	$178.8174	$178.82	$178.80	$178.80
Purchase #3	$99.62	7.238%	$106.8305	$106.83	$106.85	$106.80
Purchase #4	$76.39	8.457%	$82.8503	$82.85	$82.85	$82.90
Purchase #5	$31.31	4.333%	$32.6667	$32.67	$32.65	$32.70
Purchase #6	$57.99	13.473%	$65.803	$65.80	$65.80	$65.80
Purchase #7	$231.73	3.197%	$239.1384	$239.14	$239.15	$239.10
7 purchase totals =	$789.20		$852.5832	$852.59	$852.60	$852.60