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 $56.25   4.227%   $58.6277   $58.63   $58.65   $58.60  
  Purchase #2 $206.49   13.741%   $234.8638   $234.86   $234.85   $234.90  
  Purchase #3 $23.99   8.684%   $26.0733   $26.07   $26.05   $26.10  
  Purchase #4 $66.92   13.682%   $76.076   $76.08   $76.10   $76.10  
  Purchase #5 $28.87   9.134%   $31.507   $31.51   $31.50   $31.50  
  Purchase #6 $199.60   11.705%   $222.9632   $222.96   $222.95   $223.00  
  Purchase #7 $140.49   5.685%   $148.4769   $148.48   $148.50   $148.50  
  7 purchase totals = $722.61       $798.5879   $798.59   $798.60   $798.70