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 $209.74   11.862%   $234.6194   $234.62   $234.60   $234.60  
  Purchase #2 $34.30   10.483%   $37.8957   $37.90   $37.90   $37.90  
  Purchase #3 $241.92   13.704%   $275.0727   $275.07   $275.05   $275.10  
  Purchase #4 $47.43   13.696%   $53.926   $53.93   $53.95   $53.90  
  Purchase #5 $239.81   7.572%   $257.9684   $257.97   $257.95   $258.00  
  Purchase #6 $112.91   10.223%   $124.4528   $124.45   $124.45   $124.50  
  Purchase #7 $35.42   13.113%   $40.0646   $40.06   $40.05   $40.10  
  7 purchase totals = $921.53       $1,023.9996   $1,024.00   $1,023.95   $1,024.10