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	$140.46	3.700%	$145.657	$145.66	$145.65	$145.70
Purchase #2	$79.35	3.546%	$82.1638	$82.16	$82.15	$82.20
Purchase #3	$199.33	9.103%	$217.475	$217.48	$217.50	$217.50
Purchase #4	$81.31	10.643%	$89.9638	$89.96	$89.95	$90.00
Purchase #5	$212.39	12.460%	$238.8538	$238.85	$238.85	$238.90
Purchase #6	$35.60	3.652%	$36.9001	$36.90	$36.90	$36.90
Purchase #7	$86.57	13.785%	$98.5037	$98.50	$98.50	$98.50
7 purchase totals =	$835.01		$909.5172	$909.51	$909.50	$909.70