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 $246.78   10.227%   $272.0182   $272.02   $272.00   $272.00  
  Purchase #2 $84.51   11.860%   $94.5329   $94.53   $94.55   $94.50  
  Purchase #3 $208.90   13.566%   $237.2394   $237.24   $237.25   $237.20  
  Purchase #4 $58.32   11.686%   $65.1353   $65.14   $65.15   $65.10  
  Purchase #5 $163.49   4.293%   $170.5086   $170.51   $170.50   $170.50  
  Purchase #6 $78.41   9.520%   $85.8746   $85.87   $85.85   $85.90  
  Purchase #7 $174.56   10.565%   $193.0023   $193.00   $193.00   $193.00  
  7 purchase totals = $1,014.97       $1,118.3113   $1,118.31   $1,118.30   $1,118.20