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 $143.94   13.648%   $163.5849   $163.58   $163.60   $163.60  
  Purchase #2 $227.84   3.558%   $235.9465   $235.95   $235.95   $235.90  
  Purchase #3 $198.71   10.851%   $220.272   $220.27   $220.25   $220.30  
  Purchase #4 $236.62   8.836%   $257.5277   $257.53   $257.55   $257.50  
  Purchase #5 $44.43   7.506%   $47.7649   $47.76   $47.75   $47.80  
  Purchase #6 $250.70   11.361%   $279.182   $279.18   $279.20   $279.20  
  Purchase #7 $123.93   4.836%   $129.9233   $129.92   $129.90   $129.90  
  7 purchase totals = $1,226.17       $1,334.2013   $1,334.19   $1,334.20   $1,334.20