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 $182.39   13.727%   $207.4267   $207.43   $207.45   $207.40  
  Purchase #2 $128.26   13.205%   $145.1967   $145.20   $145.20   $145.20  
  Purchase #3 $76.93   13.471%   $87.2932   $87.29   $87.30   $87.30  
  Purchase #4 $235.62   11.307%   $262.2616   $262.26   $262.25   $262.30  
  Purchase #5 $80.25   11.730%   $89.6633   $89.66   $89.65   $89.70  
  Purchase #6 $57.87   5.823%   $61.2398   $61.24   $61.25   $61.20  
  Purchase #7 $122.87   7.193%   $131.708   $131.71   $131.70   $131.70  
  7 purchase totals = $884.19       $984.7893   $984.79   $984.80   $984.80