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 $236.33   8.624%   $256.7111   $256.71   $256.70   $256.70  
  Purchase #2 $74.51   11.742%   $83.259   $83.26   $83.25   $83.30  
  Purchase #3 $164.46   8.227%   $177.9901   $177.99   $178.00   $178.00  
  Purchase #4 $236.97   10.623%   $262.1433   $262.14   $262.15   $262.10  
  Purchase #5 $165.95   3.344%   $171.4994   $171.50   $171.50   $171.50  
  Purchase #6 $63.82   3.447%   $66.0199   $66.02   $66.00   $66.00  
  Purchase #7 $41.36   4.750%   $43.3246   $43.32   $43.30   $43.30  
  7 purchase totals = $983.40       $1,060.9474   $1,060.94   $1,060.90   $1,060.90