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 $83.93   9.521%   $91.921   $91.92   $91.90   $91.90  
  Purchase #2 $204.86   11.147%   $227.6957   $227.70   $227.70   $227.70  
  Purchase #3 $178.27   9.544%   $195.2841   $195.28   $195.30   $195.30  
  Purchase #4 $196.44   12.694%   $221.3761   $221.38   $221.40   $221.40  
  Purchase #5 $83.48   11.699%   $93.2463   $93.25   $93.25   $93.20  
  Purchase #6 $157.86   10.382%   $174.249   $174.25   $174.25   $174.20  
  Purchase #7 $46.99   10.386%   $51.8704   $51.87   $51.85   $51.90  
  7 purchase totals = $951.83       $1,055.6426   $1,055.65   $1,055.65   $1,055.60