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 $64.86   13.499%   $73.6155   $73.62   $73.60   $73.60  
  Purchase #2 $198.26   8.777%   $215.6613   $215.66   $215.65   $215.70  
  Purchase #3 $84.85   11.509%   $94.6154   $94.62   $94.60   $94.60  
  Purchase #4 $55.85   4.158%   $58.1722   $58.17   $58.15   $58.20  
  Purchase #5 $160.25   5.806%   $169.5541   $169.55   $169.55   $169.60  
  Purchase #6 $196.91   9.793%   $216.1934   $216.19   $216.20   $216.20  
  Purchase #7 $27.36   12.610%   $30.8101   $30.81   $30.80   $30.80  
  7 purchase totals = $788.34       $858.6220   $858.62   $858.55   $858.70