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 $202.71   10.728%   $224.4567   $224.46   $224.45   $224.50  
  Purchase #2 $82.54   13.356%   $93.564   $93.56   $93.55   $93.60  
  Purchase #3 $27.37   10.600%   $30.2712   $30.27   $30.25   $30.30  
  Purchase #4 $108.63   7.127%   $116.3721   $116.37   $116.35   $116.40  
  Purchase #5 $198.62   3.546%   $205.6631   $205.66   $205.65   $205.70  
  Purchase #6 $163.35   11.797%   $182.6204   $182.62   $182.60   $182.60  
  Purchase #7 $195.78   9.471%   $214.3223   $214.32   $214.30   $214.30  
  7 purchase totals = $979.00       $1,067.2698   $1,067.26   $1,067.15   $1,067.40