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 $214.58   13.810%   $244.2135   $244.21   $244.20   $244.20  
  Purchase #2 $190.82   4.483%   $199.3745   $199.37   $199.35   $199.40  
  Purchase #3 $116.39   7.256%   $124.8353   $124.84   $124.85   $124.80  
  Purchase #4 $59.84   5.434%   $63.0917   $63.09   $63.10   $63.10  
  Purchase #5 $88.63   5.153%   $93.1971   $93.20   $93.20   $93.20  
  Purchase #6 $145.62   8.681%   $158.2613   $158.26   $158.25   $158.30  
  Purchase #7 $223.27   5.211%   $234.9046   $234.90   $234.90   $234.90  
  7 purchase totals = $1,039.15       $1,117.8780   $1,117.87   $1,117.85   $1,117.90