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 $221.62   10.858%   $245.6835   $245.68   $245.70   $245.70  
  Purchase #2 $190.69   13.444%   $216.3264   $216.33   $216.35   $216.30  
  Purchase #3 $35.77   4.874%   $37.5134   $37.51   $37.50   $37.50  
  Purchase #4 $239.44   5.562%   $252.7577   $252.76   $252.75   $252.80  
  Purchase #5 $200.54   11.507%   $223.6161   $223.62   $223.60   $223.60  
  Purchase #6 $80.86   6.612%   $86.2065   $86.21   $86.20   $86.20  
  Purchase #7 $98.76   7.166%   $105.8371   $105.84   $105.85   $105.80  
  7 purchase totals = $1,067.68       $1,167.9407   $1,167.95   $1,167.95   $1,167.90