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 $249.41   7.532%   $268.1956   $268.20   $268.20   $268.20  
  Purchase #2 $69.76   4.809%   $73.1148   $73.11   $73.10   $73.10  
  Purchase #3 $138.62   4.372%   $144.6805   $144.68   $144.70   $144.70  
  Purchase #4 $96.95   11.705%   $108.298   $108.30   $108.30   $108.30  
  Purchase #5 $71.83   8.614%   $78.0174   $78.02   $78.00   $78.00  
  Purchase #6 $22.29   5.564%   $23.5302   $23.53   $23.55   $23.50  
  Purchase #7 $165.41   6.622%   $176.3635   $176.36   $176.35   $176.40  
  7 purchase totals = $814.27       $872.2000   $872.20   $872.20   $872.20