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	$94.34	12.154%	$105.8061	$105.81	$105.80	$105.80
Purchase #2	$226.83	12.181%	$254.4602	$254.46	$254.45	$254.50
Purchase #3	$72.79	11.491%	$81.1543	$81.15	$81.15	$81.20
Purchase #4	$90.29	11.642%	$100.8016	$100.80	$100.80	$100.80
Purchase #5	$155.73	13.161%	$176.2256	$176.23	$176.25	$176.20
Purchase #6	$7.28	7.214%	$7.8052	$7.81	$7.80	$7.80
Purchase #7	$69.43	11.707%	$77.5582	$77.56	$77.55	$77.60
7 purchase totals =	$716.69		$803.8112	$803.82	$803.80	$803.90