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 $201.62   3.310%   $208.2936   $208.29   $208.30   $208.30  
  Purchase #2 $23.47   13.386%   $26.6117   $26.61   $26.60   $26.60  
  Purchase #3 $21.28   3.121%   $21.9441   $21.94   $21.95   $21.90  
  Purchase #4 $117.76   3.271%   $121.6119   $121.61   $121.60   $121.60  
  Purchase #5 $238.64   8.301%   $258.4495   $258.45   $258.45   $258.40  
  Purchase #6 $246.50   10.658%   $272.772   $272.77   $272.75   $272.80  
  Purchase #7 $61.79   11.684%   $69.0095   $69.01   $69.00   $69.00  
  7 purchase totals = $911.06       $978.6923   $978.68   $978.65   $978.60