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 $60.81   12.338%   $68.3127   $68.31   $68.30   $68.30  
  Purchase #2 $236.75   8.620%   $257.1579   $257.16   $257.15   $257.20  
  Purchase #3 $207.58   10.439%   $229.2493   $229.25   $229.25   $229.20  
  Purchase #4 $63.88   7.317%   $68.5541   $68.55   $68.55   $68.60  
  Purchase #5 $107.69   6.471%   $114.6586   $114.66   $114.65   $114.70  
  Purchase #6 $250.37   4.806%   $262.4028   $262.40   $262.40   $262.40  
  Purchase #7 $201.42   12.123%   $225.8381   $225.84   $225.85   $225.80  
  7 purchase totals = $1,128.50       $1,226.1735   $1,226.17   $1,226.15   $1,226.20