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 $35.66   8.468%   $38.6797   $38.68   $38.70   $38.70  
  Purchase #2 $208.85   7.547%   $224.6119   $224.61   $224.60   $224.60  
  Purchase #3 $221.38   12.645%   $249.3735   $249.37   $249.35   $249.40  
  Purchase #4 $97.38   5.267%   $102.509   $102.51   $102.50   $102.50  
  Purchase #5 $67.38   7.111%   $72.1714   $72.17   $72.15   $72.20  
  Purchase #6 $35.73   11.426%   $39.8125   $39.81   $39.80   $39.80  
  Purchase #7 $119.57   11.257%   $133.03   $133.03   $133.05   $133.00  
  7 purchase totals = $785.95       $860.1880   $860.18   $860.15   $860.20