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 $196.56   10.192%   $216.5934   $216.59   $216.60   $216.60  
  Purchase #2 $50.39   8.204%   $54.524   $54.52   $54.50   $54.50  
  Purchase #3 $154.39   12.823%   $174.1874   $174.19   $174.20   $174.20  
  Purchase #4 $51.68   12.798%   $58.294   $58.29   $58.30   $58.30  
  Purchase #5 $207.54   3.460%   $214.7209   $214.72   $214.70   $214.70  
  Purchase #6 $15.70   13.814%   $17.8688   $17.87   $17.85   $17.90  
  Purchase #7 $211.77   13.289%   $239.9121   $239.91   $239.90   $239.90  
  7 purchase totals = $888.03       $976.1006   $976.09   $976.05   $976.10