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 $233.58   8.748%   $254.0136   $254.01   $254.00   $254.00  
  Purchase #2 $219.59   11.693%   $245.2667   $245.27   $245.25   $245.30  
  Purchase #3 $137.83   13.416%   $156.3213   $156.32   $156.30   $156.30  
  Purchase #4 $48.63   9.465%   $53.2328   $53.23   $53.25   $53.20  
  Purchase #5 $196.57   6.780%   $209.8974   $209.90   $209.90   $209.90  
  Purchase #6 $47.99   6.327%   $51.0263   $51.03   $51.05   $51.00  
  Purchase #7 $51.86   3.503%   $53.6767   $53.68   $53.70   $53.70  
  7 purchase totals = $936.05       $1,023.4348   $1,023.44   $1,023.45   $1,023.40