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 $59.94   11.261%   $66.6898   $66.69   $66.70   $66.70  
  Purchase #2 $242.44   6.247%   $257.5852   $257.59   $257.60   $257.60  
  Purchase #3 $146.92   10.831%   $162.8329   $162.83   $162.85   $162.80  
  Purchase #4 $72.66   11.301%   $80.8713   $80.87   $80.85   $80.90  
  Purchase #5 $78.49   10.180%   $86.4803   $86.48   $86.50   $86.50  
  Purchase #6 $24.36   7.153%   $26.1025   $26.10   $26.10   $26.10  
  Purchase #7 $95.49   9.703%   $104.7554   $104.76   $104.75   $104.80  
  7 purchase totals = $720.30       $785.3174   $785.32   $785.35   $785.40