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 $154.72   4.661%   $161.9315   $161.93   $161.95   $161.90  
  Purchase #2 $224.26   13.232%   $253.9341   $253.93   $253.95   $253.90  
  Purchase #3 $44.64   5.811%   $47.234   $47.23   $47.25   $47.20  
  Purchase #4 $11.70   13.193%   $13.2436   $13.24   $13.25   $13.20  
  Purchase #5 $170.82   13.397%   $193.7048   $193.70   $193.70   $193.70  
  Purchase #6 $40.69   10.136%   $44.8143   $44.81   $44.80   $44.80  
  Purchase #7 $53.96   11.187%   $59.9965   $60.00   $60.00   $60.00  
  7 purchase totals = $700.79       $774.8588   $774.84   $774.90   $774.70