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 $24.75   5.524%   $26.1172   $26.12   $26.10   $26.10  
  Purchase #2 $152.95   10.840%   $169.5298   $169.53   $169.55   $169.50  
  Purchase #3 $164.57   5.348%   $173.3712   $173.37   $173.35   $173.40  
  Purchase #4 $144.88   8.302%   $156.9079   $156.91   $156.90   $156.90  
  Purchase #5 $159.69   5.641%   $168.6981   $168.70   $168.70   $168.70  
  Purchase #6 $222.68   13.604%   $252.9734   $252.97   $252.95   $253.00  
  Purchase #7 $60.56   9.245%   $66.1588   $66.16   $66.15   $66.20  
  7 purchase totals = $930.08       $1,013.7564   $1,013.76   $1,013.70   $1,013.80