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 $232.85   12.324%   $261.5464   $261.55   $261.55   $261.50  
  Purchase #2 $112.92   3.317%   $116.6656   $116.67   $116.65   $116.70  
  Purchase #3 $11.68   6.266%   $12.4119   $12.41   $12.40   $12.40  
  Purchase #4 $91.61   11.128%   $101.8044   $101.80   $101.80   $101.80  
  Purchase #5 $83.81   13.618%   $95.2232   $95.22   $95.20   $95.20  
  Purchase #6 $105.62   11.423%   $117.685   $117.69   $117.70   $117.70  
  Purchase #7 $211.83   10.790%   $234.6865   $234.69   $234.70   $234.70  
  7 purchase totals = $850.32       $940.0230   $940.03   $940.00   $940.00