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 $228.51   13.546%   $259.464   $259.46   $259.45   $259.50  
  Purchase #2 $24.49   3.159%   $25.2636   $25.26   $25.25   $25.30  
  Purchase #3 $218.44   4.591%   $228.4686   $228.47   $228.45   $228.50  
  Purchase #4 $221.56   11.846%   $247.806   $247.81   $247.80   $247.80  
  Purchase #5 $86.70   12.202%   $97.2791   $97.28   $97.30   $97.30  
  Purchase #6 $66.55   11.103%   $73.939   $73.94   $73.95   $73.90  
  Purchase #7 $219.65   5.347%   $231.3947   $231.39   $231.40   $231.40  
  7 purchase totals = $1,065.90       $1,163.6150   $1,163.61   $1,163.60   $1,163.70