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	$156.73	7.257%	$168.1039	$168.10	$168.10	$168.10
Purchase #2	$73.89	9.198%	$80.6864	$80.69	$80.70	$80.70
Purchase #3	$39.89	7.248%	$42.7812	$42.78	$42.80	$42.80
Purchase #4	$152.90	12.472%	$171.9697	$171.97	$171.95	$172.00
Purchase #5	$78.78	6.645%	$84.0149	$84.01	$84.00	$84.00
Purchase #6	$72.58	6.867%	$77.5641	$77.56	$77.55	$77.60
Purchase #7	$132.72	8.804%	$144.4047	$144.40	$144.40	$144.40
7 purchase totals =	$707.49		$769.5249	$769.51	$769.50	$769.60