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 $104.72   8.630%   $113.7573   $113.76   $113.75   $113.80  
  Purchase #2 $64.67   3.125%   $66.6909   $66.69   $66.70   $66.70  
  Purchase #3 $238.86   11.309%   $265.8727   $265.87   $265.85   $265.90  
  Purchase #4 $95.95   12.385%   $107.8334   $107.83   $107.85   $107.80  
  Purchase #5 $111.33   11.563%   $124.2031   $124.20   $124.20   $124.20  
  Purchase #6 $227.56   8.320%   $246.493   $246.49   $246.50   $246.50  
  Purchase #7 $99.85   5.188%   $105.0302   $105.03   $105.05   $105.00  
  7 purchase totals = $942.94       $1,029.8806   $1,029.87   $1,029.90   $1,029.90