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 $68.71   10.618%   $76.0056   $76.01   $76.00   $76.00  
  Purchase #2 $221.41   8.292%   $239.7693   $239.77   $239.75   $239.80  
  Purchase #3 $248.67   10.163%   $273.9423   $273.94   $273.95   $273.90  
  Purchase #4 $182.60   13.347%   $206.9716   $206.97   $206.95   $207.00  
  Purchase #5 $108.79   12.131%   $121.9873   $121.99   $122.00   $122.00  
  Purchase #6 $160.39   6.158%   $170.2668   $170.27   $170.25   $170.30  
  Purchase #7 $150.85   3.681%   $156.4028   $156.40   $156.40   $156.40  
  7 purchase totals = $1,141.42       $1,245.3457   $1,245.35   $1,245.30   $1,245.40