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 $182.77   10.221%   $201.4509   $201.45   $201.45   $201.50  
  Purchase #2 $53.29   6.846%   $56.9382   $56.94   $56.95   $56.90  
  Purchase #3 $56.80   10.691%   $62.8725   $62.87   $62.85   $62.90  
  Purchase #4 $149.59   6.209%   $158.878   $158.88   $158.90   $158.90  
  Purchase #5 $250.82   4.221%   $261.4071   $261.41   $261.40   $261.40  
  Purchase #6 $104.94   13.406%   $119.0083   $119.01   $119.00   $119.00  
  Purchase #7 $224.49   13.396%   $254.5627   $254.56   $254.55   $254.60  
  7 purchase totals = $1,022.70       $1,115.1177   $1,115.12   $1,115.10   $1,115.20