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 $140.58   3.155%   $145.0153   $145.02   $145.00   $145.00  
  Purchase #2 $86.79   13.528%   $98.531   $98.53   $98.55   $98.50  
  Purchase #3 $179.45   10.859%   $198.9365   $198.94   $198.95   $198.90  
  Purchase #4 $72.51   13.278%   $82.1379   $82.14   $82.15   $82.10  
  Purchase #5 $23.51   12.118%   $26.3589   $26.36   $26.35   $26.40  
  Purchase #6 $248.25   5.665%   $262.3134   $262.31   $262.30   $262.30  
  Purchase #7 $183.98   7.456%   $197.6975   $197.70   $197.70   $197.70  
  7 purchase totals = $935.07       $1,010.9905   $1,011.00   $1,011.00   $1,010.90