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 $232.51   6.441%   $247.486   $247.49   $247.50   $247.50  
  Purchase #2 $63.41   6.493%   $67.5272   $67.53   $67.55   $67.50  
  Purchase #3 $162.42   11.106%   $180.4584   $180.46   $180.45   $180.50  
  Purchase #4 $245.95   3.330%   $254.1401   $254.14   $254.15   $254.10  
  Purchase #5 $232.88   13.829%   $265.085   $265.09   $265.10   $265.10  
  Purchase #6 $57.47   12.715%   $64.7773   $64.78   $64.80   $64.80  
  Purchase #7 $22.98   5.433%   $24.2285   $24.23   $24.25   $24.20  
  7 purchase totals = $1,017.62       $1,103.7025   $1,103.72   $1,103.80   $1,103.70