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 $215.66   12.361%   $242.3177   $242.32   $242.30   $242.30  
  Purchase #2 $225.51   10.596%   $249.405   $249.41   $249.40   $249.40  
  Purchase #3 $175.49   6.812%   $187.4444   $187.44   $187.45   $187.40  
  Purchase #4 $118.31   6.252%   $125.7067   $125.71   $125.70   $125.70  
  Purchase #5 $228.26   3.216%   $235.6008   $235.60   $235.60   $235.60  
  Purchase #6 $209.90   4.872%   $220.1263   $220.13   $220.15   $220.10  
  Purchase #7 $61.43   12.314%   $68.9945   $68.99   $69.00   $69.00  
  7 purchase totals = $1,234.56       $1,329.5954   $1,329.60   $1,329.60   $1,329.50