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 $44.86   8.398%   $48.6273   $48.63   $48.65   $48.60  
  Purchase #2 $151.71   12.420%   $170.5524   $170.55   $170.55   $170.60  
  Purchase #3 $125.26   5.272%   $131.8637   $131.86   $131.85   $131.90  
  Purchase #4 $219.95   7.777%   $237.0555   $237.06   $237.05   $237.10  
  Purchase #5 $154.90   12.694%   $174.563   $174.56   $174.55   $174.60  
  Purchase #6 $70.68   8.406%   $76.6214   $76.62   $76.60   $76.60  
  Purchase #7 $146.45   13.389%   $166.0582   $166.06   $166.05   $166.10  
  7 purchase totals = $913.81       $1,005.3415   $1,005.34   $1,005.30   $1,005.50