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 $162.69   3.447%   $168.2979   $168.30   $168.30   $168.30  
  Purchase #2 $30.57   10.681%   $33.8352   $33.84   $33.85   $33.80  
  Purchase #3 $248.80   6.171%   $264.1534   $264.15   $264.15   $264.20  
  Purchase #4 $24.80   7.265%   $26.6017   $26.60   $26.60   $26.60  
  Purchase #5 $195.28   5.720%   $206.45   $206.45   $206.45   $206.50  
  Purchase #6 $161.53   13.125%   $182.7308   $182.73   $182.75   $182.70  
  Purchase #7 $142.78   12.648%   $160.8388   $160.84   $160.85   $160.80  
  7 purchase totals = $966.45       $1,042.9078   $1,042.91   $1,042.95   $1,042.90