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 $190.83   12.432%   $214.554   $214.55   $214.55   $214.60  
  Purchase #2 $105.76   11.272%   $117.6813   $117.68   $117.70   $117.70  
  Purchase #3 $58.73   4.195%   $61.1937   $61.19   $61.20   $61.20  
  Purchase #4 $203.46   4.820%   $213.2668   $213.27   $213.25   $213.30  
  Purchase #5 $104.77   13.502%   $118.916   $118.92   $118.90   $118.90  
  Purchase #6 $218.91   9.846%   $240.4639   $240.46   $240.45   $240.50  
  Purchase #7 $111.54   10.457%   $123.2037   $123.20   $123.20   $123.20  
  7 purchase totals = $994.00       $1,089.2794   $1,089.27   $1,089.25   $1,089.40