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 $183.86   10.243%   $202.6928   $202.69   $202.70   $202.70  
  Purchase #2 $118.76   12.178%   $133.2226   $133.22   $133.20   $133.20  
  Purchase #3 $44.45   13.820%   $50.593   $50.59   $50.60   $50.60  
  Purchase #4 $32.29   5.798%   $34.1622   $34.16   $34.15   $34.20  
  Purchase #5 $13.29   11.465%   $14.8137   $14.81   $14.80   $14.80  
  Purchase #6 $143.32   11.852%   $160.3063   $160.31   $160.30   $160.30  
  Purchase #7 $97.30   6.741%   $103.859   $103.86   $103.85   $103.90  
  7 purchase totals = $633.27       $699.6496   $699.64   $699.60   $699.70