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 $60.26   10.267%   $66.4469   $66.45   $66.45   $66.40  
  Purchase #2 $208.66   8.840%   $227.1055   $227.11   $227.10   $227.10  
  Purchase #3 $15.45   7.416%   $16.5958   $16.60   $16.60   $16.60  
  Purchase #4 $32.43   11.748%   $36.2399   $36.24   $36.25   $36.20  
  Purchase #5 $226.25   9.331%   $247.3614   $247.36   $247.35   $247.40  
  Purchase #6 $224.84   12.393%   $252.7044   $252.70   $252.70   $252.70  
  Purchase #7 $84.83   7.111%   $90.8623   $90.86   $90.85   $90.90  
  7 purchase totals = $852.72       $937.3162   $937.32   $937.30   $937.30