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 $159.77   3.402%   $165.2054   $165.21   $165.20   $165.20  
  Purchase #2 $54.72   5.219%   $57.5758   $57.58   $57.60   $57.60  
  Purchase #3 $186.26   5.102%   $195.763   $195.76   $195.75   $195.80  
  Purchase #4 $14.95   3.477%   $15.4698   $15.47   $15.45   $15.50  
  Purchase #5 $121.83   7.527%   $131.0001   $131.00   $131.00   $131.00  
  Purchase #6 $197.63   13.340%   $223.9938   $223.99   $224.00   $224.00  
  Purchase #7 $208.92   11.501%   $232.9479   $232.95   $232.95   $232.90  
  7 purchase totals = $944.08       $1,021.9558   $1,021.96   $1,021.95   $1,022.00