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 $77.89   12.477%   $87.6083   $87.61   $87.60   $87.60  
  Purchase #2 $96.60   8.215%   $104.5357   $104.54   $104.55   $104.50  
  Purchase #3 $59.85   3.396%   $61.8825   $61.88   $61.90   $61.90  
  Purchase #4 $135.56   5.261%   $142.6918   $142.69   $142.70   $142.70  
  Purchase #5 $118.96   12.786%   $134.1702   $134.17   $134.15   $134.20  
  Purchase #6 $82.87   3.103%   $85.4415   $85.44   $85.45   $85.40  
  Purchase #7 $211.84   11.814%   $236.8668   $236.87   $236.85   $236.90  
  7 purchase totals = $783.57       $853.1968   $853.20   $853.20   $853.20