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 $61.63   10.382%   $68.0284   $68.03   $68.05   $68.00  
  Purchase #2 $226.99   12.451%   $255.2525   $255.25   $255.25   $255.30  
  Purchase #3 $108.63   13.135%   $122.8986   $122.90   $122.90   $122.90  
  Purchase #4 $117.88   4.271%   $122.9147   $122.91   $122.90   $122.90  
  Purchase #5 $186.89   7.697%   $201.2749   $201.27   $201.25   $201.30  
  Purchase #6 $103.56   4.766%   $108.4957   $108.50   $108.50   $108.50  
  Purchase #7 $225.86   11.228%   $251.2196   $251.22   $251.20   $251.20  
  7 purchase totals = $1,031.44       $1,130.0844   $1,130.08   $1,130.05   $1,130.10