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 $69.58   10.242%   $76.7064   $76.71   $76.70   $76.70  
  Purchase #2 $10.90   4.189%   $11.3566   $11.36   $11.35   $11.40  
  Purchase #3 $15.96   12.737%   $17.9928   $17.99   $18.00   $18.00  
  Purchase #4 $232.67   4.125%   $242.2676   $242.27   $242.25   $242.30  
  Purchase #5 $241.71   9.716%   $265.1945   $265.19   $265.20   $265.20  
  Purchase #6 $156.87   9.389%   $171.5985   $171.60   $171.60   $171.60  
  Purchase #7 $44.47   11.528%   $49.5965   $49.60   $49.60   $49.60  
  7 purchase totals = $772.16       $834.7129   $834.72   $834.70   $834.80