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 $190.67   6.134%   $202.3657   $202.37   $202.35   $202.40  
  Purchase #2 $57.66   11.312%   $64.1825   $64.18   $64.20   $64.20  
  Purchase #3 $71.92   12.732%   $81.0769   $81.08   $81.10   $81.10  
  Purchase #4 $221.98   8.157%   $240.0869   $240.09   $240.10   $240.10  
  Purchase #5 $241.75   11.462%   $269.4594   $269.46   $269.45   $269.50  
  Purchase #6 $31.53   11.792%   $35.248   $35.25   $35.25   $35.20  
  Purchase #7 $57.38   11.374%   $63.9064   $63.91   $63.90   $63.90  
  7 purchase totals = $872.89       $956.3258   $956.34   $956.35   $956.40