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 $240.25   5.636%   $253.7905   $253.79   $253.80   $253.80  
  Purchase #2 $149.71   10.347%   $165.2005   $165.20   $165.20   $165.20  
  Purchase #3 $62.35   5.872%   $66.0112   $66.01   $66.00   $66.00  
  Purchase #4 $214.77   3.315%   $221.8896   $221.89   $221.90   $221.90  
  Purchase #5 $80.77   12.268%   $90.6789   $90.68   $90.70   $90.70  
  Purchase #6 $114.90   4.637%   $120.2279   $120.23   $120.25   $120.20  
  Purchase #7 $250.97   7.537%   $269.8856   $269.89   $269.90   $269.90  
  7 purchase totals = $1,113.72       $1,187.6842   $1,187.69   $1,187.75   $1,187.70