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 $229.44   7.213%   $245.9895   $245.99   $246.00   $246.00  
  Purchase #2 $40.82   13.420%   $46.298   $46.30   $46.30   $46.30  
  Purchase #3 $86.34   10.549%   $95.448   $95.45   $95.45   $95.40  
  Purchase #4 $85.88   10.736%   $95.1001   $95.10   $95.10   $95.10  
  Purchase #5 $171.37   11.414%   $190.9302   $190.93   $190.95   $190.90  
  Purchase #6 $249.68   3.475%   $258.3564   $258.36   $258.35   $258.40  
  Purchase #7 $165.61   6.623%   $176.5784   $176.58   $176.60   $176.60  
  7 purchase totals = $1,029.14       $1,108.7006   $1,108.71   $1,108.75   $1,108.70