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 $108.53   12.638%   $122.246   $122.25   $122.25   $122.20  
  Purchase #2 $69.31   6.396%   $73.7431   $73.74   $73.75   $73.70  
  Purchase #3 $24.68   7.718%   $26.5848   $26.58   $26.60   $26.60  
  Purchase #4 $109.83   10.844%   $121.74   $121.74   $121.75   $121.70  
  Purchase #5 $56.82   3.233%   $58.657   $58.66   $58.65   $58.70  
  Purchase #6 $129.75   9.203%   $141.6909   $141.69   $141.70   $141.70  
  Purchase #7 $29.37   5.799%   $31.0732   $31.07   $31.05   $31.10  
  7 purchase totals = $528.29       $575.7350   $575.73   $575.75   $575.70