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 $61.95   11.727%   $69.2149   $69.21   $69.20   $69.20  
  Purchase #2 $98.73   12.749%   $111.3171   $111.32   $111.30   $111.30  
  Purchase #3 $66.98   3.571%   $69.3719   $69.37   $69.35   $69.40  
  Purchase #4 $70.47   5.358%   $74.2458   $74.25   $74.25   $74.20  
  Purchase #5 $136.33   13.161%   $154.2724   $154.27   $154.25   $154.30  
  Purchase #6 $104.57   7.156%   $112.053   $112.05   $112.05   $112.10  
  Purchase #7 $239.63   12.402%   $269.3489   $269.35   $269.35   $269.30  
  7 purchase totals = $778.66       $859.8240   $859.82   $859.75   $859.80