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 $32.46   10.228%   $35.78   $35.78   $35.80   $35.80  
  Purchase #2 $237.52   10.161%   $261.6544   $261.65   $261.65   $261.70  
  Purchase #3 $210.77   10.389%   $232.6669   $232.67   $232.65   $232.70  
  Purchase #4 $66.84   10.368%   $73.77   $73.77   $73.75   $73.80  
  Purchase #5 $115.77   11.221%   $128.7606   $128.76   $128.75   $128.80  
  Purchase #6 $199.69   3.318%   $206.3157   $206.32   $206.30   $206.30  
  Purchase #7 $34.99   6.847%   $37.3858   $37.39   $37.40   $37.40  
  7 purchase totals = $898.04       $976.3334   $976.34   $976.30   $976.50