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 $57.92   9.202%   $63.2498   $63.25   $63.25   $63.20  
  Purchase #2 $140.79   10.808%   $156.0066   $156.01   $156.00   $156.00  
  Purchase #3 $153.97   4.359%   $160.6816   $160.68   $160.70   $160.70  
  Purchase #4 $197.62   5.680%   $208.8448   $208.84   $208.85   $208.80  
  Purchase #5 $186.33   4.324%   $194.3869   $194.39   $194.40   $194.40  
  Purchase #6 $169.73   12.344%   $190.6815   $190.68   $190.70   $190.70  
  Purchase #7 $47.56   7.285%   $51.0247   $51.02   $51.00   $51.00  
  7 purchase totals = $953.92       $1,024.8759   $1,024.87   $1,024.90   $1,024.80