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 $237.78   5.308%   $250.4014   $250.40   $250.40   $250.40  
  Purchase #2 $182.93   12.564%   $205.9133   $205.91   $205.90   $205.90  
  Purchase #3 $41.54   13.403%   $47.1076   $47.11   $47.10   $47.10  
  Purchase #4 $57.86   11.579%   $64.5596   $64.56   $64.55   $64.60  
  Purchase #5 $235.60   11.737%   $263.2524   $263.25   $263.25   $263.30  
  Purchase #6 $220.57   10.697%   $244.1644   $244.16   $244.15   $244.20  
  Purchase #7 $156.79   12.543%   $176.4562   $176.46   $176.45   $176.50  
  7 purchase totals = $1,133.07       $1,251.8549   $1,251.85   $1,251.80   $1,252.00