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 $232.95   13.651%   $264.75   $264.75   $264.75   $264.80  
  Purchase #2 $182.54   9.504%   $199.8886   $199.89   $199.90   $199.90  
  Purchase #3 $16.40   4.134%   $17.078   $17.08   $17.10   $17.10  
  Purchase #4 $21.42   9.779%   $23.5147   $23.51   $23.50   $23.50  
  Purchase #5 $54.63   13.391%   $61.9455   $61.95   $61.95   $61.90  
  Purchase #6 $141.32   6.412%   $150.3814   $150.38   $150.40   $150.40  
  Purchase #7 $102.45   9.819%   $112.5096   $112.51   $112.50   $112.50  
  7 purchase totals = $751.71       $830.0678   $830.07   $830.10   $830.10