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 $13.68   5.628%   $14.4499   $14.45   $14.45   $14.40  
  Purchase #2 $96.50   6.271%   $102.5515   $102.55   $102.55   $102.60  
  Purchase #3 $63.55   5.786%   $67.227   $67.23   $67.25   $67.20  
  Purchase #4 $156.78   5.806%   $165.8826   $165.88   $165.90   $165.90  
  Purchase #5 $8.95   10.796%   $9.9162   $9.92   $9.90   $9.90  
  Purchase #6 $138.50   7.757%   $149.2434   $149.24   $149.25   $149.20  
  Purchase #7 $107.54   9.227%   $117.4627   $117.46   $117.45   $117.50  
  7 purchase totals = $585.50       $626.7333   $626.73   $626.75   $626.70