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 $24.30   7.517%   $26.1266   $26.13   $26.15   $26.10  
  Purchase #2 $165.81   6.549%   $176.6689   $176.67   $176.65   $176.70  
  Purchase #3 $52.38   10.126%   $57.684   $57.68   $57.70   $57.70  
  Purchase #4 $157.68   5.527%   $166.395   $166.40   $166.40   $166.40  
  Purchase #5 $53.68   5.412%   $56.5852   $56.59   $56.60   $56.60  
  Purchase #6 $94.96   3.265%   $98.0604   $98.06   $98.05   $98.10  
  Purchase #7 $153.93   9.252%   $168.1716   $168.17   $168.15   $168.20  
  7 purchase totals = $702.74       $749.6917   $749.70   $749.70   $749.80