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 $66.87   3.279%   $69.0627   $69.06   $69.05   $69.10  
  Purchase #2 $9.69   12.543%   $10.9054   $10.91   $10.90   $10.90  
  Purchase #3 $114.66   8.721%   $124.6595   $124.66   $124.65   $124.70  
  Purchase #4 $87.31   7.853%   $94.1665   $94.17   $94.15   $94.20  
  Purchase #5 $238.46   4.432%   $249.0285   $249.03   $249.05   $249.00  
  Purchase #6 $111.28   10.109%   $122.5293   $122.53   $122.55   $122.50  
  Purchase #7 $188.59   13.810%   $214.6343   $214.63   $214.65   $214.60  
  7 purchase totals = $816.86       $884.9862   $884.99   $885.00   $885.00