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 $55.88   12.203%   $62.699   $62.70   $62.70   $62.70  
  Purchase #2 $48.55   6.285%   $51.6014   $51.60   $51.60   $51.60  
  Purchase #3 $120.81   4.433%   $126.1655   $126.17   $126.15   $126.20  
  Purchase #4 $154.99   9.277%   $169.3684   $169.37   $169.35   $169.40  
  Purchase #5 $151.47   12.587%   $170.5355   $170.54   $170.55   $170.50  
  Purchase #6 $177.96   11.761%   $198.8899   $198.89   $198.90   $198.90  
  Purchase #7 $70.51   4.371%   $73.592   $73.59   $73.60   $73.60  
  7 purchase totals = $780.17       $852.8517   $852.86   $852.85   $852.90