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 $60.69   6.523%   $64.6488   $64.65   $64.65   $64.60  
  Purchase #2 $179.77   11.851%   $201.0745   $201.07   $201.05   $201.10  
  Purchase #3 $122.60   11.804%   $137.0717   $137.07   $137.05   $137.10  
  Purchase #4 $148.90   10.511%   $164.5509   $164.55   $164.55   $164.60  
  Purchase #5 $245.49   4.701%   $257.0305   $257.03   $257.05   $257.00  
  Purchase #6 $80.84   11.682%   $90.2837   $90.28   $90.30   $90.30  
  Purchase #7 $216.95   5.354%   $228.5655   $228.57   $228.55   $228.60  
  7 purchase totals = $1,055.24       $1,143.2256   $1,143.22   $1,143.20   $1,143.30