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 $181.70   13.627%   $206.4603   $206.46   $206.45   $206.50  
  Purchase #2 $106.32   9.579%   $116.5044   $116.50   $116.50   $116.50  
  Purchase #3 $23.33   13.693%   $26.5246   $26.52   $26.50   $26.50  
  Purchase #4 $145.57   8.583%   $158.0643   $158.06   $158.05   $158.10  
  Purchase #5 $214.83   13.812%   $244.5023   $244.50   $244.50   $244.50  
  Purchase #6 $170.86   8.727%   $185.771   $185.77   $185.75   $185.80  
  Purchase #7 $248.83   6.676%   $265.4419   $265.44   $265.45   $265.40  
  7 purchase totals = $1,091.44       $1,203.2688   $1,203.25   $1,203.20   $1,203.30