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 $245.27   6.612%   $261.4873   $261.49   $261.50   $261.50  
  Purchase #2 $41.67   5.117%   $43.8023   $43.80   $43.80   $43.80  
  Purchase #3 $139.61   7.231%   $149.7052   $149.71   $149.70   $149.70  
  Purchase #4 $216.44   9.147%   $236.2378   $236.24   $236.25   $236.20  
  Purchase #5 $75.83   7.596%   $81.59   $81.59   $81.60   $81.60  
  Purchase #6 $88.58   5.323%   $93.2951   $93.30   $93.30   $93.30  
  Purchase #7 $242.91   3.235%   $250.7681   $250.77   $250.75   $250.80  
  7 purchase totals = $1,050.31       $1,116.8858   $1,116.90   $1,116.90   $1,116.90