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 $234.39   8.673%   $254.7186   $254.72   $254.70   $254.70  
  Purchase #2 $29.25   11.357%   $32.5719   $32.57   $32.55   $32.60  
  Purchase #3 $23.38   8.870%   $25.4538   $25.45   $25.45   $25.50  
  Purchase #4 $195.69   10.851%   $216.9243   $216.92   $216.90   $216.90  
  Purchase #5 $177.66   13.174%   $201.0649   $201.06   $201.05   $201.10  
  Purchase #6 $71.27   3.561%   $73.8079   $73.81   $73.80   $73.80  
  Purchase #7 $242.88   11.853%   $271.6686   $271.67   $271.65   $271.70  
  7 purchase totals = $974.52       $1,076.2100   $1,076.20   $1,076.10   $1,076.30