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 $61.80   6.757%   $65.9758   $65.98   $66.00   $66.00  
  Purchase #2 $108.36   10.265%   $119.4832   $119.48   $119.50   $119.50  
  Purchase #3 $24.75   3.778%   $25.6851   $25.69   $25.70   $25.70  
  Purchase #4 $9.63   8.113%   $10.4113   $10.41   $10.40   $10.40  
  Purchase #5 $246.59   6.272%   $262.0561   $262.06   $262.05   $262.10  
  Purchase #6 $157.51   11.461%   $175.5622   $175.56   $175.55   $175.60  
  Purchase #7 $148.43   5.615%   $156.7643   $156.76   $156.75   $156.80  
  7 purchase totals = $757.07       $815.9380   $815.94   $815.95   $816.10