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	$64.83	3.175%	$66.8884	$66.89	$66.90	$66.90
Purchase #2	$114.99	11.188%	$127.8551	$127.86	$127.85	$127.90
Purchase #3	$216.37	13.104%	$244.7231	$244.72	$244.70	$244.70
Purchase #4	$143.42	9.198%	$156.6118	$156.61	$156.60	$156.60
Purchase #5	$84.80	7.700%	$91.3296	$91.33	$91.35	$91.30
Purchase #6	$95.92	6.797%	$102.4397	$102.44	$102.45	$102.40
Purchase #7	$167.48	5.192%	$176.1756	$176.18	$176.20	$176.20
7 purchase totals =	$887.81		$966.0233	$966.03	$966.05	$966.00