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 $161.46   9.788%   $177.2637   $177.26   $177.25   $177.30  
  Purchase #2 $211.78   3.613%   $219.4316   $219.43   $219.45   $219.40  
  Purchase #3 $152.98   5.105%   $160.7896   $160.79   $160.80   $160.80  
  Purchase #4 $22.93   9.683%   $25.1503   $25.15   $25.15   $25.20  
  Purchase #5 $154.46   10.268%   $170.32   $170.32   $170.30   $170.30  
  Purchase #6 $248.72   10.571%   $275.0122   $275.01   $275.00   $275.00  
  Purchase #7 $163.36   7.612%   $175.795   $175.80   $175.80   $175.80  
  7 purchase totals = $1,115.69       $1,203.7624   $1,203.76   $1,203.75   $1,203.80