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 $36.33   12.856%   $41.0006   $41.00   $41.00   $41.00  
  Purchase #2 $22.71   5.698%   $24.004   $24.00   $24.00   $24.00  
  Purchase #3 $5.68   6.451%   $6.0464   $6.05   $6.05   $6.00  
  Purchase #4 $181.80   4.660%   $190.2719   $190.27   $190.25   $190.30  
  Purchase #5 $171.36   12.790%   $193.2769   $193.28   $193.30   $193.30  
  Purchase #6 $232.40   10.131%   $255.9444   $255.94   $255.95   $255.90  
  Purchase #7 $108.57   13.544%   $123.2747   $123.27   $123.25   $123.30  
  7 purchase totals = $758.85       $833.8189   $833.81   $833.80   $833.80