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 $10.44   11.370%   $11.627   $11.63   $11.65   $11.60  
  Purchase #2 $22.82   8.163%   $24.6828   $24.68   $24.70   $24.70  
  Purchase #3 $250.99   8.713%   $272.8588   $272.86   $272.85   $272.90  
  Purchase #4 $188.48   13.274%   $213.4988   $213.50   $213.50   $213.50  
  Purchase #5 $88.90   10.195%   $97.9634   $97.96   $97.95   $98.00  
  Purchase #6 $98.45   5.229%   $103.598   $103.60   $103.60   $103.60  
  Purchase #7 $217.31   12.747%   $245.0105   $245.01   $245.00   $245.00  
  7 purchase totals = $877.39       $969.2393   $969.24   $969.25   $969.30