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 $141.47   10.612%   $156.4828   $156.48   $156.50   $156.50  
  Purchase #2 $103.62   10.181%   $114.1696   $114.17   $114.15   $114.20  
  Purchase #3 $104.32   9.551%   $114.2836   $114.28   $114.30   $114.30  
  Purchase #4 $244.58   4.262%   $255.004   $255.00   $255.00   $255.00  
  Purchase #5 $8.89   13.465%   $10.087   $10.09   $10.10   $10.10  
  Purchase #6 $57.86   9.746%   $63.499   $63.50   $63.50   $63.50  
  Purchase #7 $86.37   8.327%   $93.562   $93.56   $93.55   $93.60  
  7 purchase totals = $747.11       $807.0880   $807.08   $807.10   $807.20