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 $235.46   13.622%   $267.5344   $267.53   $267.55   $267.50  
  Purchase #2 $171.27   11.379%   $190.7588   $190.76   $190.75   $190.80  
  Purchase #3 $7.63   12.173%   $8.5588   $8.56   $8.55   $8.60  
  Purchase #4 $225.31   9.324%   $246.3179   $246.32   $246.30   $246.30  
  Purchase #5 $171.80   12.828%   $193.8385   $193.84   $193.85   $193.80  
  Purchase #6 $114.71   4.655%   $120.0498   $120.05   $120.05   $120.00  
  Purchase #7 $194.73   10.166%   $214.5263   $214.53   $214.55   $214.50  
  7 purchase totals = $1,120.91       $1,241.5845   $1,241.59   $1,241.60   $1,241.50