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	$246.26	3.181%	$254.0935	$254.09	$254.10	$254.10
Purchase #2	$99.34	8.867%	$108.1485	$108.15	$108.15	$108.10
Purchase #3	$243.95	10.635%	$269.8941	$269.89	$269.90	$269.90
Purchase #4	$76.44	8.413%	$82.8709	$82.87	$82.85	$82.90
Purchase #5	$18.28	12.725%	$20.6061	$20.61	$20.60	$20.60
Purchase #6	$148.70	13.615%	$168.9455	$168.95	$168.95	$168.90
Purchase #7	$49.99	10.169%	$55.0735	$55.07	$55.05	$55.10
7 purchase totals =	$882.96		$959.6321	$959.63	$959.60	$959.60