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 $11.35   11.459%   $12.6506   $12.65   $12.65   $12.70  
  Purchase #2 $194.99   6.672%   $207.9997   $208.00   $208.00   $208.00  
  Purchase #3 $105.76   7.212%   $113.3874   $113.39   $113.40   $113.40  
  Purchase #4 $154.62   8.667%   $168.0209   $168.02   $168.00   $168.00  
  Purchase #5 $172.46   13.597%   $195.9094   $195.91   $195.90   $195.90  
  Purchase #6 $153.54   7.346%   $164.819   $164.82   $164.80   $164.80  
  Purchase #7 $197.35   8.262%   $213.6551   $213.66   $213.65   $213.70  
  7 purchase totals = $990.07       $1,076.4421   $1,076.45   $1,076.40   $1,076.50