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 $33.68   4.463%   $35.1831   $35.18   $35.20   $35.20  
  Purchase #2 $221.40   6.347%   $235.4523   $235.45   $235.45   $235.50  
  Purchase #3 $244.96   4.264%   $255.4051   $255.41   $255.40   $255.40  
  Purchase #4 $194.54   5.482%   $205.2047   $205.20   $205.20   $205.20  
  Purchase #5 $246.69   8.110%   $266.6966   $266.70   $266.70   $266.70  
  Purchase #6 $102.83   11.569%   $114.7264   $114.73   $114.75   $114.70  
  Purchase #7 $247.48   11.115%   $274.9874   $274.99   $275.00   $275.00  
  7 purchase totals = $1,291.58       $1,387.6556   $1,387.66   $1,387.70   $1,387.70