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 $76.38   10.320%   $84.2624   $84.26   $84.25   $84.30  
  Purchase #2 $102.66   10.447%   $113.3849   $113.38   $113.40   $113.40  
  Purchase #3 $64.70   12.622%   $72.8664   $72.87   $72.85   $72.90  
  Purchase #4 $153.38   4.454%   $160.2115   $160.21   $160.20   $160.20  
  Purchase #5 $108.58   8.400%   $117.7007   $117.70   $117.70   $117.70  
  Purchase #6 $36.77   11.315%   $40.9305   $40.93   $40.95   $40.90  
  Purchase #7 $174.44   12.547%   $196.327   $196.33   $196.35   $196.30  
  7 purchase totals = $716.91       $785.6834   $785.68   $785.70   $785.70