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 $51.70   9.490%   $56.6063   $56.61   $56.60   $56.60  
  Purchase #2 $85.73   9.468%   $93.8469   $93.85   $93.85   $93.80  
  Purchase #3 $157.67   10.661%   $174.4792   $174.48   $174.50   $174.50  
  Purchase #4 $87.62   11.461%   $97.6621   $97.66   $97.65   $97.70  
  Purchase #5 $208.66   12.346%   $234.4212   $234.42   $234.40   $234.40  
  Purchase #6 $168.54   8.712%   $183.2232   $183.22   $183.20   $183.20  
  Purchase #7 $198.29   11.803%   $221.6942   $221.69   $221.70   $221.70  
  7 purchase totals = $958.21       $1,061.9331   $1,061.93   $1,061.90   $1,061.90