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 $86.95   11.558%   $96.9997   $97.00   $97.00   $97.00  
  Purchase #2 $114.61   4.402%   $119.6551   $119.66   $119.65   $119.70  
  Purchase #3 $187.79   10.685%   $207.8554   $207.86   $207.85   $207.90  
  Purchase #4 $173.79   7.153%   $186.2212   $186.22   $186.20   $186.20  
  Purchase #5 $130.90   4.552%   $136.8586   $136.86   $136.85   $136.90  
  Purchase #6 $179.47   9.406%   $196.3509   $196.35   $196.35   $196.40  
  Purchase #7 $66.84   3.382%   $69.1005   $69.10   $69.10   $69.10  
  7 purchase totals = $940.35       $1,013.0414   $1,013.05   $1,013.00   $1,013.20