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 $15.31   12.564%   $17.2335   $17.23   $17.25   $17.20  
  Purchase #2 $210.95   5.792%   $223.1682   $223.17   $223.15   $223.20  
  Purchase #3 $220.27   4.242%   $229.6139   $229.61   $229.60   $229.60  
  Purchase #4 $85.39   11.403%   $95.127   $95.13   $95.15   $95.10  
  Purchase #5 $41.86   11.551%   $46.6952   $46.70   $46.70   $46.70  
  Purchase #6 $168.77   3.347%   $174.4187   $174.42   $174.40   $174.40  
  Purchase #7 $106.75   3.265%   $110.2354   $110.24   $110.25   $110.20  
  7 purchase totals = $849.30       $896.4919   $896.50   $896.50   $896.40