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	$74.47	4.119%	$77.5374	$77.54	$77.55	$77.50
Purchase #2	$127.77	13.145%	$144.5654	$144.57	$144.55	$144.60
Purchase #3	$92.57	9.241%	$101.1244	$101.12	$101.10	$101.10
Purchase #4	$196.45	10.734%	$217.5369	$217.54	$217.55	$217.50
Purchase #5	$20.89	4.312%	$21.7908	$21.79	$21.80	$21.80
Purchase #6	$30.39	4.238%	$31.6779	$31.68	$31.70	$31.70
Purchase #7	$10.51	11.563%	$11.7253	$11.73	$11.75	$11.70
7 purchase totals =	$553.05		$605.9581	$605.97	$606.00	$605.90