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 $8.67   6.769%   $9.2569   $9.26   $9.25   $9.30  
  Purchase #2 $62.97   3.587%   $65.2287   $65.23   $65.25   $65.20  
  Purchase #3 $149.92   8.652%   $162.8911   $162.89   $162.90   $162.90  
  Purchase #4 $241.95   9.421%   $264.7441   $264.74   $264.75   $264.70  
  Purchase #5 $242.60   6.503%   $258.3763   $258.38   $258.40   $258.40  
  Purchase #6 $157.70   6.684%   $168.2407   $168.24   $168.25   $168.20  
  Purchase #7 $13.50   4.818%   $14.1504   $14.15   $14.15   $14.20  
  7 purchase totals = $877.31       $942.8882   $942.89   $942.95   $942.90