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 $239.83   8.852%   $261.0598   $261.06   $261.05   $261.10  
  Purchase #2 $33.56   8.705%   $36.4814   $36.48   $36.50   $36.50  
  Purchase #3 $6.45   8.820%   $7.0189   $7.02   $7.00   $7.00  
  Purchase #4 $123.90   5.153%   $130.2846   $130.28   $130.30   $130.30  
  Purchase #5 $196.62   5.813%   $208.0495   $208.05   $208.05   $208.00  
  Purchase #6 $118.56   10.213%   $130.6685   $130.67   $130.65   $130.70  
  Purchase #7 $224.35   11.816%   $250.8592   $250.86   $250.85   $250.90  
  7 purchase totals = $943.27       $1,024.4219   $1,024.42   $1,024.40   $1,024.50