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 $208.27   11.500%   $232.2211   $232.22   $232.20   $232.20  
  Purchase #2 $235.80   13.583%   $267.8287   $267.83   $267.85   $267.80  
  Purchase #3 $133.95   12.853%   $151.1666   $151.17   $151.15   $151.20  
  Purchase #4 $86.68   10.857%   $96.0908   $96.09   $96.10   $96.10  
  Purchase #5 $249.27   5.802%   $263.7326   $263.73   $263.75   $263.70  
  Purchase #6 $19.95   11.544%   $22.253   $22.25   $22.25   $22.30  
  Purchase #7 $149.39   12.787%   $168.4925   $168.49   $168.50   $168.50  
  7 purchase totals = $1,083.31       $1,201.7853   $1,201.78   $1,201.80   $1,201.80