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 $26.66   3.295%   $27.5384   $27.54   $27.55   $27.50  
  Purchase #2 $196.90   3.422%   $203.6379   $203.64   $203.65   $203.60  
  Purchase #3 $162.63   4.805%   $170.4444   $170.44   $170.45   $170.40  
  Purchase #4 $105.74   8.540%   $114.7702   $114.77   $114.75   $114.80  
  Purchase #5 $181.65   8.105%   $196.3727   $196.37   $196.35   $196.40  
  Purchase #6 $180.84   13.866%   $205.9153   $205.92   $205.90   $205.90  
  Purchase #7 $241.58   8.459%   $262.0153   $262.02   $262.00   $262.00  
  7 purchase totals = $1,096.00       $1,180.6942   $1,180.70   $1,180.65   $1,180.60