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 $62.86   10.250%   $69.3032   $69.30   $69.30   $69.30  
  Purchase #2 $134.77   3.327%   $139.2538   $139.25   $139.25   $139.30  
  Purchase #3 $128.40   5.116%   $134.9689   $134.97   $134.95   $135.00  
  Purchase #4 $67.63   12.218%   $75.893   $75.89   $75.90   $75.90  
  Purchase #5 $214.62   5.147%   $225.6665   $225.67   $225.65   $225.70  
  Purchase #6 $128.69   9.209%   $140.5411   $140.54   $140.55   $140.50  
  Purchase #7 $179.29   11.386%   $199.704   $199.70   $199.70   $199.70  
  7 purchase totals = $916.26       $985.3305   $985.32   $985.30   $985.40