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 $214.32   10.459%   $236.7357   $236.74   $236.75   $236.70  
  Purchase #2 $163.38   12.179%   $183.2781   $183.28   $183.30   $183.30  
  Purchase #3 $128.69   11.354%   $143.3015   $143.30   $143.30   $143.30  
  Purchase #4 $33.73   3.341%   $34.8569   $34.86   $34.85   $34.90  
  Purchase #5 $76.26   6.133%   $80.937   $80.94   $80.95   $80.90  
  Purchase #6 $174.93   13.509%   $198.5613   $198.56   $198.55   $198.60  
  Purchase #7 $8.36   5.486%   $8.8186   $8.82   $8.80   $8.80  
  7 purchase totals = $799.67       $886.4891   $886.50   $886.50   $886.50