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 $243.85   5.475%   $257.2008   $257.20   $257.20   $257.20  
  Purchase #2 $19.99   11.287%   $22.2463   $22.25   $22.25   $22.20  
  Purchase #3 $222.69   11.849%   $249.0765   $249.08   $249.10   $249.10  
  Purchase #4 $211.54   3.296%   $218.5124   $218.51   $218.50   $218.50  
  Purchase #5 $56.53   5.705%   $59.755   $59.76   $59.75   $59.80  
  Purchase #6 $164.71   12.553%   $185.386   $185.39   $185.40   $185.40  
  Purchase #7 $215.94   7.695%   $232.5566   $232.56   $232.55   $232.60  
  7 purchase totals = $1,135.25       $1,224.7336   $1,224.75   $1,224.75   $1,224.80