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 $86.48   8.333%   $93.6864   $93.69   $93.70   $93.70  
  Purchase #2 $125.84   10.811%   $139.4446   $139.44   $139.45   $139.40  
  Purchase #3 $128.44   3.300%   $132.6785   $132.68   $132.70   $132.70  
  Purchase #4 $205.70   3.436%   $212.7679   $212.77   $212.75   $212.80  
  Purchase #5 $61.75   5.649%   $65.2383   $65.24   $65.25   $65.20  
  Purchase #6 $118.47   12.676%   $133.4873   $133.49   $133.50   $133.50  
  Purchase #7 $19.83   4.342%   $20.691   $20.69   $20.70   $20.70  
  7 purchase totals = $746.51       $797.9940   $798.00   $798.05   $798.00