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 $145.93   8.423%   $158.2217   $158.22   $158.20   $158.20  
  Purchase #2 $144.40   10.241%   $159.188   $159.19   $159.20   $159.20  
  Purchase #3 $163.75   9.745%   $179.7074   $179.71   $179.70   $179.70  
  Purchase #4 $15.94   8.169%   $17.2421   $17.24   $17.25   $17.20  
  Purchase #5 $113.60   3.621%   $117.7135   $117.71   $117.70   $117.70  
  Purchase #6 $118.31   4.595%   $123.7463   $123.75   $123.75   $123.70  
  Purchase #7 $221.63   13.362%   $251.2442   $251.24   $251.25   $251.20  
  7 purchase totals = $923.56       $1,007.0632   $1,007.06   $1,007.05   $1,006.90