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 $46.53   10.258%   $51.303   $51.30   $51.30   $51.30  
  Purchase #2 $54.50   13.593%   $61.9082   $61.91   $61.90   $61.90  
  Purchase #3 $66.57   4.225%   $69.3826   $69.38   $69.40   $69.40  
  Purchase #4 $105.62   13.329%   $119.6981   $119.70   $119.70   $119.70  
  Purchase #5 $198.39   8.692%   $215.6341   $215.63   $215.65   $215.60  
  Purchase #6 $227.72   8.806%   $247.773   $247.77   $247.75   $247.80  
  Purchase #7 $72.88   13.445%   $82.6787   $82.68   $82.70   $82.70  
  7 purchase totals = $772.21       $848.3777   $848.37   $848.40   $848.40