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 $224.46   6.791%   $239.7031   $239.70   $239.70   $239.70  
  Purchase #2 $106.34   3.288%   $109.8365   $109.84   $109.85   $109.80  
  Purchase #3 $70.31   4.420%   $73.4177   $73.42   $73.40   $73.40  
  Purchase #4 $196.84   11.110%   $218.7089   $218.71   $218.70   $218.70  
  Purchase #5 $234.65   7.798%   $252.948   $252.95   $252.95   $252.90  
  Purchase #6 $70.92   8.483%   $76.9361   $76.94   $76.95   $76.90  
  Purchase #7 $190.44   7.207%   $204.165   $204.17   $204.15   $204.20  
  7 purchase totals = $1,093.96       $1,175.7153   $1,175.73   $1,175.70   $1,175.60