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 $180.84   11.163%   $201.0272   $201.03   $201.05   $201.00  
  Purchase #2 $117.85   13.751%   $134.0556   $134.06   $134.05   $134.10  
  Purchase #3 $76.43   12.857%   $86.2566   $86.26   $86.25   $86.30  
  Purchase #4 $186.26   10.144%   $205.1542   $205.15   $205.15   $205.20  
  Purchase #5 $45.25   12.714%   $51.0031   $51.00   $51.00   $51.00  
  Purchase #6 $82.98   13.622%   $94.2835   $94.28   $94.30   $94.30  
  Purchase #7 $54.61   10.327%   $60.2496   $60.25   $60.25   $60.20  
  7 purchase totals = $744.22       $832.0298   $832.03   $832.05   $832.10