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 $68.69   8.715%   $74.6763   $74.68   $74.70   $74.70  
  Purchase #2 $213.55   4.188%   $222.4935   $222.49   $222.50   $222.50  
  Purchase #3 $50.53   4.662%   $52.8857   $52.89   $52.90   $52.90  
  Purchase #4 $14.27   9.381%   $15.6087   $15.61   $15.60   $15.60  
  Purchase #5 $239.29   6.847%   $255.6742   $255.67   $255.65   $255.70  
  Purchase #6 $89.68   9.617%   $98.3045   $98.30   $98.30   $98.30  
  Purchase #7 $242.77   6.394%   $258.2927   $258.29   $258.30   $258.30  
  7 purchase totals = $918.78       $977.9356   $977.93   $977.95   $978.00