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 $61.40   8.188%   $66.4274   $66.43   $66.45   $66.40  
  Purchase #2 $241.37   7.324%   $259.0479   $259.05   $259.05   $259.00  
  Purchase #3 $219.27   4.574%   $229.2994   $229.30   $229.30   $229.30  
  Purchase #4 $135.61   4.486%   $141.6935   $141.69   $141.70   $141.70  
  Purchase #5 $32.33   5.108%   $33.9814   $33.98   $34.00   $34.00  
  Purchase #6 $195.46   7.448%   $210.0179   $210.02   $210.00   $210.00  
  Purchase #7 $200.60   13.113%   $226.9047   $226.90   $226.90   $226.90  
  7 purchase totals = $1,086.04       $1,167.3722   $1,167.37   $1,167.40   $1,167.30