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 $33.83   12.600%   $38.0926   $38.09   $38.10   $38.10  
  Purchase #2 $107.93   13.681%   $122.6959   $122.70   $122.70   $122.70  
  Purchase #3 $21.32   13.501%   $24.1984   $24.20   $24.20   $24.20  
  Purchase #4 $80.27   7.841%   $86.564   $86.56   $86.55   $86.60  
  Purchase #5 $107.56   11.483%   $119.9111   $119.91   $119.90   $119.90  
  Purchase #6 $38.44   3.299%   $39.7081   $39.71   $39.70   $39.70  
  Purchase #7 $33.48   4.311%   $34.9233   $34.92   $34.90   $34.90  
  7 purchase totals = $422.83       $466.0934   $466.09   $466.05   $466.10