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 $56.92   10.810%   $63.0731   $63.07   $63.05   $63.10  
  Purchase #2 $84.75   11.233%   $94.27   $94.27   $94.25   $94.30  
  Purchase #3 $206.95   8.414%   $224.3628   $224.36   $224.35   $224.40  
  Purchase #4 $55.51   11.766%   $62.0413   $62.04   $62.05   $62.00  
  Purchase #5 $162.62   13.698%   $184.8957   $184.90   $184.90   $184.90  
  Purchase #6 $25.98   6.274%   $27.61   $27.61   $27.60   $27.60  
  Purchase #7 $24.94   4.656%   $26.1012   $26.10   $26.10   $26.10  
  7 purchase totals = $617.67       $682.3541   $682.35   $682.30   $682.40