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 $243.85   7.425%   $261.9559   $261.96   $261.95   $262.00  
  Purchase #2 $91.30   11.347%   $101.6598   $101.66   $101.65   $101.70  
  Purchase #3 $36.51   8.150%   $39.4856   $39.49   $39.50   $39.50  
  Purchase #4 $64.97   9.584%   $71.1967   $71.20   $71.20   $71.20  
  Purchase #5 $232.99   10.213%   $256.7853   $256.79   $256.80   $256.80  
  Purchase #6 $56.63   3.111%   $58.3918   $58.39   $58.40   $58.40  
  Purchase #7 $41.31   13.336%   $46.8191   $46.82   $46.80   $46.80  
  7 purchase totals = $767.56       $836.2942   $836.31   $836.30   $836.40