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 $86.95   10.571%   $96.1415   $96.14   $96.15   $96.10  
  Purchase #2 $61.76   10.329%   $68.1392   $68.14   $68.15   $68.10  
  Purchase #3 $66.56   6.241%   $70.714   $70.71   $70.70   $70.70  
  Purchase #4 $135.70   13.613%   $154.1728   $154.17   $154.15   $154.20  
  Purchase #5 $234.50   11.202%   $260.7687   $260.77   $260.75   $260.80  
  Purchase #6 $98.37   6.855%   $105.1133   $105.11   $105.10   $105.10  
  Purchase #7 $201.73   8.428%   $218.7318   $218.73   $218.75   $218.70  
  7 purchase totals = $885.57       $973.7813   $973.77   $973.75   $973.70