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 $236.99   10.459%   $261.7768   $261.78   $261.80   $261.80  
  Purchase #2 $132.97   9.814%   $146.0197   $146.02   $146.00   $146.00  
  Purchase #3 $56.93   11.823%   $63.6608   $63.66   $63.65   $63.70  
  Purchase #4 $131.57   9.179%   $143.6468   $143.65   $143.65   $143.60  
  Purchase #5 $79.70   6.314%   $84.7323   $84.73   $84.75   $84.70  
  Purchase #6 $208.46   6.211%   $221.4075   $221.41   $221.40   $221.40  
  Purchase #7 $52.94   3.147%   $54.606   $54.61   $54.60   $54.60  
  7 purchase totals = $899.56       $975.8499   $975.86   $975.85   $975.80