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 $24.76   5.178%   $26.0421   $26.04   $26.05   $26.00  
  Purchase #2 $175.87   3.803%   $182.5583   $182.56   $182.55   $182.60  
  Purchase #3 $229.69   5.206%   $241.6477   $241.65   $241.65   $241.60  
  Purchase #4 $199.99   7.821%   $215.6312   $215.63   $215.65   $215.60  
  Purchase #5 $112.28   7.740%   $120.9705   $120.97   $120.95   $121.00  
  Purchase #6 $205.49   12.426%   $231.0242   $231.02   $231.00   $231.00  
  Purchase #7 $214.94   7.864%   $231.8429   $231.84   $231.85   $231.80  
  7 purchase totals = $1,163.02       $1,249.7169   $1,249.71   $1,249.70   $1,249.60