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 $67.58   7.597%   $72.7141   $72.71   $72.70   $72.70  
  Purchase #2 $175.31   9.866%   $192.6061   $192.61   $192.60   $192.60  
  Purchase #3 $141.25   5.706%   $149.3097   $149.31   $149.30   $149.30  
  Purchase #4 $163.44   11.788%   $182.7063   $182.71   $182.70   $182.70  
  Purchase #5 $192.73   12.169%   $216.1833   $216.18   $216.20   $216.20  
  Purchase #6 $77.48   12.471%   $87.1425   $87.14   $87.15   $87.10  
  Purchase #7 $156.46   6.547%   $166.7034   $166.70   $166.70   $166.70  
  7 purchase totals = $974.25       $1,067.3654   $1,067.36   $1,067.35   $1,067.30