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 $201.37   8.555%   $218.5972   $218.60   $218.60   $218.60  
  Purchase #2 $136.49   5.757%   $144.3477   $144.35   $144.35   $144.30  
  Purchase #3 $62.71   3.167%   $64.696   $64.70   $64.70   $64.70  
  Purchase #4 $221.97   3.739%   $230.2695   $230.27   $230.25   $230.30  
  Purchase #5 $244.92   10.631%   $270.9574   $270.96   $270.95   $271.00  
  Purchase #6 $92.46   6.573%   $98.5374   $98.54   $98.55   $98.50  
  Purchase #7 $212.45   7.116%   $227.5679   $227.57   $227.55   $227.60  
  7 purchase totals = $1,172.37       $1,254.9731   $1,254.99   $1,254.95   $1,255.00