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 $184.98   6.252%   $196.5449   $196.54   $196.55   $196.50  
  Purchase #2 $73.99   13.694%   $84.1222   $84.12   $84.10   $84.10  
  Purchase #3 $186.67   8.329%   $202.2177   $202.22   $202.20   $202.20  
  Purchase #4 $233.37   7.335%   $250.4877   $250.49   $250.50   $250.50  
  Purchase #5 $5.85   8.660%   $6.3566   $6.36   $6.35   $6.40  
  Purchase #6 $35.91   7.776%   $38.7024   $38.70   $38.70   $38.70  
  Purchase #7 $131.66   8.378%   $142.6905   $142.69   $142.70   $142.70  
  7 purchase totals = $852.43       $921.1220   $921.12   $921.10   $921.10