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 $247.26   8.228%   $267.6046   $267.60   $267.60   $267.60  
  Purchase #2 $43.46   7.388%   $46.6708   $46.67   $46.65   $46.70  
  Purchase #3 $165.61   10.749%   $183.4114   $183.41   $183.40   $183.40  
  Purchase #4 $247.51   7.761%   $266.7193   $266.72   $266.70   $266.70  
  Purchase #5 $84.30   8.118%   $91.1435   $91.14   $91.15   $91.10  
  Purchase #6 $248.76   8.595%   $270.1409   $270.14   $270.15   $270.10  
  Purchase #7 $141.98   7.826%   $153.0914   $153.09   $153.10   $153.10  
  7 purchase totals = $1,178.88       $1,278.7819   $1,278.77   $1,278.75   $1,278.70