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 $20.79   4.169%   $21.6567   $21.66   $21.65   $21.70  
  Purchase #2 $244.75   6.734%   $261.2315   $261.23   $261.25   $261.20  
  Purchase #3 $249.91   12.604%   $281.4087   $281.41   $281.40   $281.40  
  Purchase #4 $79.80   7.354%   $85.6685   $85.67   $85.65   $85.70  
  Purchase #5 $185.43   11.446%   $206.6543   $206.65   $206.65   $206.70  
  Purchase #6 $45.46   6.829%   $48.5645   $48.56   $48.55   $48.60  
  Purchase #7 $197.39   5.783%   $208.8051   $208.81   $208.80   $208.80  
  7 purchase totals = $1,023.53       $1,113.9893   $1,113.99   $1,113.95   $1,114.10