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 $62.93   5.870%   $66.624   $66.62   $66.60   $66.60  
  Purchase #2 $205.28   11.361%   $228.6019   $228.60   $228.60   $228.60  
  Purchase #3 $195.80   12.683%   $220.6333   $220.63   $220.65   $220.60  
  Purchase #4 $146.47   8.473%   $158.8804   $158.88   $158.90   $158.90  
  Purchase #5 $231.93   3.266%   $239.5048   $239.50   $239.50   $239.50  
  Purchase #6 $82.47   3.636%   $85.4686   $85.47   $85.45   $85.50  
  Purchase #7 $7.26   10.115%   $7.9943   $7.99   $8.00   $8.00  
  7 purchase totals = $932.14       $1,007.7073   $1,007.69   $1,007.70   $1,007.70