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 $59.29   13.508%   $67.2989   $67.30   $67.30   $67.30  
  Purchase #2 $239.32   7.742%   $257.8482   $257.85   $257.85   $257.80  
  Purchase #3 $250.91   4.367%   $261.8672   $261.87   $261.85   $261.90  
  Purchase #4 $48.26   8.579%   $52.4002   $52.40   $52.40   $52.40  
  Purchase #5 $152.72   7.672%   $164.4367   $164.44   $164.45   $164.40  
  Purchase #6 $212.25   11.536%   $236.7352   $236.74   $236.75   $236.70  
  Purchase #7 $159.54   6.652%   $170.1526   $170.15   $170.15   $170.20  
  7 purchase totals = $1,122.29       $1,210.7390   $1,210.75   $1,210.75   $1,210.70