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 $35.33   5.157%   $37.152   $37.15   $37.15   $37.20  
  Purchase #2 $221.53   6.857%   $236.7203   $236.72   $236.70   $236.70  
  Purchase #3 $24.85   10.786%   $27.5303   $27.53   $27.55   $27.50  
  Purchase #4 $119.27   11.517%   $133.0063   $133.01   $133.00   $133.00  
  Purchase #5 $175.67   4.161%   $182.9796   $182.98   $183.00   $183.00  
  Purchase #6 $62.98   3.796%   $65.3707   $65.37   $65.35   $65.40  
  Purchase #7 $180.59   10.845%   $200.175   $200.18   $200.20   $200.20  
  7 purchase totals = $820.22       $882.9342   $882.94   $882.95   $883.00