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 $207.56   8.253%   $224.6899   $224.69   $224.70   $224.70  
  Purchase #2 $11.58   11.473%   $12.9086   $12.91   $12.90   $12.90  
  Purchase #3 $104.26   9.761%   $114.4368   $114.44   $114.45   $114.40  
  Purchase #4 $92.52   6.433%   $98.4718   $98.47   $98.45   $98.50  
  Purchase #5 $107.72   10.760%   $119.3107   $119.31   $119.30   $119.30  
  Purchase #6 $110.43   11.167%   $122.7617   $122.76   $122.75   $122.80  
  Purchase #7 $6.72   10.638%   $7.4349   $7.43   $7.45   $7.40  
  7 purchase totals = $640.79       $700.0144   $700.01   $700.00   $700.00