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 $86.76   8.582%   $94.2057   $94.21   $94.20   $94.20  
  Purchase #2 $232.39   13.186%   $263.0329   $263.03   $263.05   $263.00  
  Purchase #3 $43.72   8.811%   $47.5722   $47.57   $47.55   $47.60  
  Purchase #4 $134.77   5.104%   $141.6487   $141.65   $141.65   $141.60  
  Purchase #5 $91.28   12.200%   $102.4162   $102.42   $102.40   $102.40  
  Purchase #6 $79.90   7.366%   $85.7854   $85.79   $85.80   $85.80  
  Purchase #7 $60.81   11.703%   $67.9266   $67.93   $67.95   $67.90  
  7 purchase totals = $729.63       $802.5877   $802.60   $802.60   $802.50