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 $125.25   7.200%   $134.268   $134.27   $134.25   $134.30  
  Purchase #2 $226.30   11.772%   $252.94   $252.94   $252.95   $252.90  
  Purchase #3 $156.88   8.334%   $169.9544   $169.95   $169.95   $170.00  
  Purchase #4 $220.29   13.351%   $249.7009   $249.70   $249.70   $249.70  
  Purchase #5 $177.89   10.681%   $196.8904   $196.89   $196.90   $196.90  
  Purchase #6 $131.94   7.256%   $141.5136   $141.51   $141.50   $141.50  
  Purchase #7 $216.74   11.631%   $241.949   $241.95   $241.95   $241.90  
  7 purchase totals = $1,255.29       $1,387.2163   $1,387.21   $1,387.20   $1,387.20