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	$72.44	5.125%	$76.1526	$76.15	$76.15	$76.20
Purchase #2	$90.38	10.537%	$99.9033	$99.90	$99.90	$99.90
Purchase #3	$69.70	12.232%	$78.2257	$78.23	$78.25	$78.20
Purchase #4	$229.47	13.691%	$260.8867	$260.89	$260.90	$260.90
Purchase #5	$239.95	6.128%	$254.6541	$254.65	$254.65	$254.70
Purchase #6	$150.85	13.209%	$170.7758	$170.78	$170.80	$170.80
Purchase #7	$87.97	12.368%	$98.8501	$98.85	$98.85	$98.90
7 purchase totals =	$940.76		$1,039.4483	$1,039.45	$1,039.50	$1,039.60