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 $45.80   7.756%   $49.3522   $49.35   $49.35   $49.40  
  Purchase #2 $250.88   4.120%   $261.2163   $261.22   $261.20   $261.20  
  Purchase #3 $93.39   11.200%   $103.8497   $103.85   $103.85   $103.80  
  Purchase #4 $124.86   11.439%   $139.1427   $139.14   $139.15   $139.10  
  Purchase #5 $23.53   13.412%   $26.6858   $26.69   $26.70   $26.70  
  Purchase #6 $249.51   13.211%   $282.4728   $282.47   $282.45   $282.50  
  Purchase #7 $81.75   12.115%   $91.654   $91.65   $91.65   $91.70  
  7 purchase totals = $869.72       $954.3735   $954.37   $954.35   $954.40