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 $63.97   11.839%   $71.5434   $71.54   $71.55   $71.50  
  Purchase #2 $49.57   11.661%   $55.3504   $55.35   $55.35   $55.40  
  Purchase #3 $36.46   5.867%   $38.5991   $38.60   $38.60   $38.60  
  Purchase #4 $70.42   8.246%   $76.2268   $76.23   $76.25   $76.20  
  Purchase #5 $216.25   4.724%   $226.4657   $226.47   $226.45   $226.50  
  Purchase #6 $122.57   8.449%   $132.9259   $132.93   $132.95   $132.90  
  Purchase #7 $164.71   9.396%   $180.1862   $180.19   $180.20   $180.20  
  7 purchase totals = $723.95       $781.2975   $781.31   $781.35   $781.30