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 $176.51   12.818%   $199.1351   $199.14   $199.15   $199.10  
  Purchase #2 $162.25   9.499%   $177.6621   $177.66   $177.65   $177.70  
  Purchase #3 $9.45   13.368%   $10.7133   $10.71   $10.70   $10.70  
  Purchase #4 $95.55   9.780%   $104.8948   $104.89   $104.90   $104.90  
  Purchase #5 $57.48   7.792%   $61.9588   $61.96   $61.95   $62.00  
  Purchase #6 $140.44   12.175%   $157.5386   $157.54   $157.55   $157.50  
  Purchase #7 $34.46   5.277%   $36.2785   $36.28   $36.30   $36.30  
  7 purchase totals = $676.14       $748.1812   $748.18   $748.20   $748.20