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 $54.48   4.341%   $56.845   $56.85   $56.85   $56.80  
  Purchase #2 $117.94   6.208%   $125.2617   $125.26   $125.25   $125.30  
  Purchase #3 $23.75   9.767%   $26.0697   $26.07   $26.05   $26.10  
  Purchase #4 $168.84   8.843%   $183.7705   $183.77   $183.75   $183.80  
  Purchase #5 $146.55   9.607%   $160.6291   $160.63   $160.65   $160.60  
  Purchase #6 $85.65   8.236%   $92.7041   $92.70   $92.70   $92.70  
  Purchase #7 $197.58   8.414%   $214.2044   $214.20   $214.20   $214.20  
  7 purchase totals = $794.79       $859.4845   $859.48   $859.45   $859.50