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 $84.72   13.611%   $96.2512   $96.25   $96.25   $96.30  
  Purchase #2 $41.32   8.211%   $44.7128   $44.71   $44.70   $44.70  
  Purchase #3 $140.84   12.740%   $158.783   $158.78   $158.80   $158.80  
  Purchase #4 $226.92   5.405%   $239.185   $239.19   $239.20   $239.20  
  Purchase #5 $158.44   11.536%   $176.7176   $176.72   $176.70   $176.70  
  Purchase #6 $127.91   11.454%   $142.5608   $142.56   $142.55   $142.60  
  Purchase #7 $11.27   3.759%   $11.6936   $11.69   $11.70   $11.70  
  7 purchase totals = $791.42       $869.9040   $869.90   $869.90   $870.00