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 $153.77   9.293%   $168.0598   $168.06   $168.05   $168.10  
  Purchase #2 $190.51   9.466%   $208.5437   $208.54   $208.55   $208.50  
  Purchase #3 $30.59   6.535%   $32.5891   $32.59   $32.60   $32.60  
  Purchase #4 $241.76   11.286%   $269.045   $269.05   $269.05   $269.00  
  Purchase #5 $15.26   6.536%   $16.2574   $16.26   $16.25   $16.30  
  Purchase #6 $224.74   3.429%   $232.4463   $232.45   $232.45   $232.40  
  Purchase #7 $173.48   4.546%   $181.3664   $181.37   $181.35   $181.40  
  7 purchase totals = $1,030.11       $1,108.3077   $1,108.32   $1,108.30   $1,108.30