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 $76.64   12.274%   $86.0468   $86.05   $86.05   $86.00  
  Purchase #2 $177.87   7.785%   $191.7172   $191.72   $191.70   $191.70  
  Purchase #3 $209.37   7.328%   $224.7126   $224.71   $224.70   $224.70  
  Purchase #4 $152.35   9.437%   $166.7273   $166.73   $166.75   $166.70  
  Purchase #5 $14.30   5.124%   $15.0327   $15.03   $15.05   $15.00  
  Purchase #6 $154.36   12.667%   $173.9128   $173.91   $173.90   $173.90  
  Purchase #7 $43.49   12.728%   $49.0254   $49.03   $49.05   $49.00  
  7 purchase totals = $828.38       $907.1748   $907.18   $907.20   $907.00