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 $117.79   4.747%   $123.3815   $123.38   $123.40   $123.40  
  Purchase #2 $15.82   11.382%   $17.6206   $17.62   $17.60   $17.60  
  Purchase #3 $13.82   13.311%   $15.6596   $15.66   $15.65   $15.70  
  Purchase #4 $129.48   11.514%   $144.3883   $144.39   $144.40   $144.40  
  Purchase #5 $74.99   3.681%   $77.7504   $77.75   $77.75   $77.80  
  Purchase #6 $83.76   5.796%   $88.6147   $88.61   $88.60   $88.60  
  Purchase #7 $221.49   4.611%   $231.7029   $231.70   $231.70   $231.70  
  7 purchase totals = $657.15       $699.1180   $699.11   $699.10   $699.20