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	$37.73	13.229%	$42.7213	$42.72	$42.70	$42.70
Purchase #2	$65.77	5.713%	$69.5274	$69.53	$69.55	$69.50
Purchase #3	$166.86	3.722%	$173.0705	$173.07	$173.05	$173.10
Purchase #4	$155.48	10.596%	$171.9547	$171.95	$171.95	$172.00
Purchase #5	$68.66	7.525%	$73.8267	$73.83	$73.85	$73.80
Purchase #6	$56.71	3.531%	$58.7124	$58.71	$58.70	$58.70
Purchase #7	$69.98	11.478%	$78.0123	$78.01	$78.00	$78.00
7 purchase totals =	$621.19		$667.8253	$667.82	$667.80	$667.80