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 $56.30   8.772%   $61.2386   $61.24   $61.25   $61.20  
  Purchase #2 $178.41   13.504%   $202.5025   $202.50   $202.50   $202.50  
  Purchase #3 $214.81   6.391%   $228.5385   $228.54   $228.55   $228.50  
  Purchase #4 $227.72   4.282%   $237.471   $237.47   $237.45   $237.50  
  Purchase #5 $207.54   10.354%   $229.0287   $229.03   $229.05   $229.00  
  Purchase #6 $62.58   7.330%   $67.1671   $67.17   $67.15   $67.20  
  Purchase #7 $232.77   4.856%   $244.0733   $244.07   $244.05   $244.10  
  7 purchase totals = $1,180.13       $1,270.0197   $1,270.02   $1,270.00   $1,270.00