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 $60.62   8.861%   $65.9915   $65.99   $66.00   $66.00  
  Purchase #2 $53.63   6.547%   $57.1412   $57.14   $57.15   $57.10  
  Purchase #3 $186.37   5.709%   $197.0099   $197.01   $197.00   $197.00  
  Purchase #4 $238.37   11.782%   $266.4548   $266.45   $266.45   $266.50  
  Purchase #5 $157.63   13.482%   $178.8817   $178.88   $178.90   $178.90  
  Purchase #6 $152.72   7.609%   $164.3405   $164.34   $164.35   $164.30  
  Purchase #7 $239.45   10.727%   $265.1358   $265.14   $265.15   $265.10  
  7 purchase totals = $1,088.79       $1,194.9554   $1,194.95   $1,195.00   $1,194.90