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 $226.77   10.563%   $250.7237   $250.72   $250.70   $250.70  
  Purchase #2 $129.97   3.630%   $134.6879   $134.69   $134.70   $134.70  
  Purchase #3 $36.27   9.516%   $39.7215   $39.72   $39.70   $39.70  
  Purchase #4 $76.51   12.440%   $86.0278   $86.03   $86.05   $86.00  
  Purchase #5 $98.68   7.185%   $105.7702   $105.77   $105.75   $105.80  
  Purchase #6 $167.30   6.285%   $177.8148   $177.81   $177.80   $177.80  
  Purchase #7 $201.46   13.429%   $228.5141   $228.51   $228.50   $228.50  
  7 purchase totals = $936.96       $1,023.2600   $1,023.25   $1,023.20   $1,023.20