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 $233.89   11.869%   $261.6504   $261.65   $261.65   $261.70  
  Purchase #2 $181.40   13.223%   $205.3865   $205.39   $205.40   $205.40  
  Purchase #3 $8.45   9.621%   $9.263   $9.26   $9.25   $9.30  
  Purchase #4 $21.51   4.792%   $22.5408   $22.54   $22.55   $22.50  
  Purchase #5 $199.25   5.739%   $210.685   $210.69   $210.70   $210.70  
  Purchase #6 $117.76   3.865%   $122.3114   $122.31   $122.30   $122.30  
  Purchase #7 $64.26   11.636%   $71.7373   $71.74   $71.75   $71.70  
  7 purchase totals = $826.52       $903.5744   $903.58   $903.60   $903.60