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 $212.97   6.681%   $227.1985   $227.20   $227.20   $227.20  
  Purchase #2 $249.96   9.793%   $274.4386   $274.44   $274.45   $274.40  
  Purchase #3 $248.87   11.165%   $276.6563   $276.66   $276.65   $276.70  
  Purchase #4 $146.33   10.429%   $161.5908   $161.59   $161.60   $161.60  
  Purchase #5 $86.27   4.411%   $90.0754   $90.08   $90.10   $90.10  
  Purchase #6 $189.74   5.345%   $199.8816   $199.88   $199.90   $199.90  
  Purchase #7 $36.45   6.465%   $38.8065   $38.81   $38.80   $38.80  
  7 purchase totals = $1,170.59       $1,268.6477   $1,268.66   $1,268.70   $1,268.70