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 $116.28   5.796%   $123.0196   $123.02   $123.00   $123.00  
  Purchase #2 $8.48   9.450%   $9.2814   $9.28   $9.30   $9.30  
  Purchase #3 $69.63   10.189%   $76.7246   $76.72   $76.70   $76.70  
  Purchase #4 $23.72   12.433%   $26.6691   $26.67   $26.65   $26.70  
  Purchase #5 $121.70   8.279%   $131.7755   $131.78   $131.80   $131.80  
  Purchase #6 $193.63   7.437%   $208.0303   $208.03   $208.05   $208.00  
  Purchase #7 $220.64   9.118%   $240.758   $240.76   $240.75   $240.80  
  7 purchase totals = $754.08       $816.2585   $816.26   $816.25   $816.30