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 $244.64   10.347%   $269.9529   $269.95   $269.95   $270.00  
  Purchase #2 $142.69   13.274%   $161.6307   $161.63   $161.65   $161.60  
  Purchase #3 $52.39   4.140%   $54.5589   $54.56   $54.55   $54.60  
  Purchase #4 $61.80   12.526%   $69.5411   $69.54   $69.55   $69.50  
  Purchase #5 $28.32   8.350%   $30.6847   $30.68   $30.70   $30.70  
  Purchase #6 $53.82   3.748%   $55.8372   $55.84   $55.85   $55.80  
  Purchase #7 $78.67   5.537%   $83.026   $83.03   $83.05   $83.00  
  7 purchase totals = $662.33       $725.2315   $725.23   $725.30   $725.20