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 $246.43   8.553%   $267.5072   $267.51   $267.50   $267.50  
  Purchase #2 $236.26   5.286%   $248.7487   $248.75   $248.75   $248.70  
  Purchase #3 $102.30   6.234%   $108.6774   $108.68   $108.70   $108.70  
  Purchase #4 $69.88   12.243%   $78.4354   $78.44   $78.45   $78.40  
  Purchase #5 $234.25   4.119%   $243.8988   $243.90   $243.90   $243.90  
  Purchase #6 $237.35   3.141%   $244.8052   $244.81   $244.80   $244.80  
  Purchase #7 $177.54   8.180%   $192.0628   $192.06   $192.05   $192.10  
  7 purchase totals = $1,304.01       $1,384.1355   $1,384.15   $1,384.15   $1,384.10