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 $227.88   10.735%   $252.3429   $252.34   $252.35   $252.30  
  Purchase #2 $55.72   11.162%   $61.9395   $61.94   $61.95   $61.90  
  Purchase #3 $44.49   9.493%   $48.7134   $48.71   $48.70   $48.70  
  Purchase #4 $124.50   7.381%   $133.6893   $133.69   $133.70   $133.70  
  Purchase #5 $92.73   11.531%   $103.4227   $103.42   $103.40   $103.40  
  Purchase #6 $128.30   7.848%   $138.369   $138.37   $138.35   $138.40  
  Purchase #7 $34.58   10.390%   $38.1729   $38.17   $38.15   $38.20  
  7 purchase totals = $708.20       $776.6497   $776.64   $776.60   $776.60