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 $181.36   12.206%   $203.4968   $203.50   $203.50   $203.50  
  Purchase #2 $196.39   9.505%   $215.0569   $215.06   $215.05   $215.10  
  Purchase #3 $30.76   6.853%   $32.868   $32.87   $32.85   $32.90  
  Purchase #4 $155.99   6.579%   $166.2526   $166.25   $166.25   $166.30  
  Purchase #5 $237.31   11.405%   $264.3752   $264.38   $264.40   $264.40  
  Purchase #6 $163.96   13.703%   $186.4274   $186.43   $186.45   $186.40  
  Purchase #7 $248.37   4.305%   $259.0623   $259.06   $259.05   $259.10  
  7 purchase totals = $1,214.14       $1,327.5392   $1,327.55   $1,327.55   $1,327.70