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 $247.25   8.671%   $268.689   $268.69   $268.70   $268.70  
  Purchase #2 $60.87   12.777%   $68.6474   $68.65   $68.65   $68.60  
  Purchase #3 $246.86   6.304%   $262.4221   $262.42   $262.40   $262.40  
  Purchase #4 $14.78   13.612%   $16.7919   $16.79   $16.80   $16.80  
  Purchase #5 $242.26   5.549%   $255.703   $255.70   $255.70   $255.70  
  Purchase #6 $248.86   4.122%   $259.118   $259.12   $259.10   $259.10  
  Purchase #7 $95.60   3.648%   $99.0875   $99.09   $99.10   $99.10  
  7 purchase totals = $1,156.48       $1,230.4589   $1,230.46   $1,230.45   $1,230.40