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 $65.57   12.601%   $73.8325   $73.83   $73.85   $73.80  
  Purchase #2 $226.99   6.289%   $241.2654   $241.27   $241.25   $241.30  
  Purchase #3 $232.44   11.566%   $259.324   $259.32   $259.30   $259.30  
  Purchase #4 $10.37   7.515%   $11.1493   $11.15   $11.15   $11.10  
  Purchase #5 $125.33   6.281%   $133.202   $133.20   $133.20   $133.20  
  Purchase #6 $38.30   11.465%   $42.6911   $42.69   $42.70   $42.70  
  Purchase #7 $67.60   3.115%   $69.7057   $69.71   $69.70   $69.70  
  7 purchase totals = $766.60       $831.1700   $831.17   $831.15   $831.10