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 $184.31   13.669%   $209.5033   $209.50   $209.50   $209.50  
  Purchase #2 $98.44   4.460%   $102.8304   $102.83   $102.85   $102.80  
  Purchase #3 $134.99   5.859%   $142.8991   $142.90   $142.90   $142.90  
  Purchase #4 $69.60   12.261%   $78.1337   $78.13   $78.15   $78.10  
  Purchase #5 $41.58   5.131%   $43.7135   $43.71   $43.70   $43.70  
  Purchase #6 $121.65   3.388%   $125.7715   $125.77   $125.75   $125.80  
  Purchase #7 $50.44   6.226%   $53.5804   $53.58   $53.60   $53.60  
  7 purchase totals = $701.01       $756.4319   $756.42   $756.45   $756.40