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 $30.78   5.446%   $32.4563   $32.46   $32.45   $32.50  
  Purchase #2 $206.34   3.653%   $213.8776   $213.88   $213.90   $213.90  
  Purchase #3 $234.32   11.430%   $261.1028   $261.10   $261.10   $261.10  
  Purchase #4 $112.54   9.615%   $123.3607   $123.36   $123.35   $123.40  
  Purchase #5 $114.51   7.586%   $123.1967   $123.20   $123.20   $123.20  
  Purchase #6 $205.47   5.131%   $216.0127   $216.01   $216.00   $216.00  
  Purchase #7 $54.79   3.213%   $56.5504   $56.55   $56.55   $56.60  
  7 purchase totals = $958.75       $1,026.5572   $1,026.56   $1,026.55   $1,026.70