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 $58.81   6.853%   $62.8402   $62.84   $62.85   $62.80  
  Purchase #2 $126.70   3.396%   $131.0027   $131.00   $131.00   $131.00  
  Purchase #3 $207.64   13.736%   $236.1614   $236.16   $236.15   $236.20  
  Purchase #4 $185.52   13.772%   $211.0698   $211.07   $211.05   $211.10  
  Purchase #5 $81.88   11.745%   $91.4968   $91.50   $91.50   $91.50  
  Purchase #6 $57.63   13.208%   $65.2418   $65.24   $65.25   $65.20  
  Purchase #7 $31.49   13.430%   $35.7191   $35.72   $35.70   $35.70  
  7 purchase totals = $749.67       $833.5318   $833.53   $833.50   $833.50