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 $133.26   11.611%   $148.7328   $148.73   $148.75   $148.70  
  Purchase #2 $23.77   13.365%   $26.9469   $26.95   $26.95   $26.90  
  Purchase #3 $168.68   6.245%   $179.2141   $179.21   $179.20   $179.20  
  Purchase #4 $186.64   10.634%   $206.4873   $206.49   $206.50   $206.50  
  Purchase #5 $68.96   12.158%   $77.3442   $77.34   $77.35   $77.30  
  Purchase #6 $175.43   11.569%   $195.7255   $195.73   $195.75   $195.70  
  Purchase #7 $82.83   8.658%   $90.0014   $90.00   $90.00   $90.00  
  7 purchase totals = $839.57       $924.4522   $924.45   $924.50   $924.30