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 $162.83   13.197%   $184.3187   $184.32   $184.30   $184.30  
  Purchase #2 $184.84   3.553%   $191.4074   $191.41   $191.40   $191.40  
  Purchase #3 $57.67   11.783%   $64.4653   $64.47   $64.45   $64.50  
  Purchase #4 $199.75   3.705%   $207.1507   $207.15   $207.15   $207.20  
  Purchase #5 $24.95   6.651%   $26.6094   $26.61   $26.60   $26.60  
  Purchase #6 $225.42   10.189%   $248.388   $248.39   $248.40   $248.40  
  Purchase #7 $140.31   13.264%   $158.9207   $158.92   $158.90   $158.90  
  7 purchase totals = $995.77       $1,081.2602   $1,081.27   $1,081.20   $1,081.30