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 $95.71   6.592%   $102.0192   $102.02   $102.00   $102.00  
  Purchase #2 $193.27   8.314%   $209.3385   $209.34   $209.35   $209.30  
  Purchase #3 $36.88   9.305%   $40.3117   $40.31   $40.30   $40.30  
  Purchase #4 $34.78   11.326%   $38.7192   $38.72   $38.70   $38.70  
  Purchase #5 $157.34   11.817%   $175.9329   $175.93   $175.95   $175.90  
  Purchase #6 $33.96   5.813%   $35.9341   $35.93   $35.95   $35.90  
  Purchase #7 $249.63   3.452%   $258.2472   $258.25   $258.25   $258.20  
  7 purchase totals = $801.57       $860.5028   $860.50   $860.50   $860.30