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 $60.36   11.530%   $67.3195   $67.32   $67.30   $67.30  
  Purchase #2 $32.25   10.572%   $35.6595   $35.66   $35.65   $35.70  
  Purchase #3 $23.74   13.335%   $26.9057   $26.91   $26.90   $26.90  
  Purchase #4 $82.67   5.115%   $86.8986   $86.90   $86.90   $86.90  
  Purchase #5 $25.94   6.286%   $27.5706   $27.57   $27.55   $27.60  
  Purchase #6 $229.49   3.800%   $238.2106   $238.21   $238.20   $238.20  
  Purchase #7 $237.49   4.676%   $248.595   $248.60   $248.60   $248.60  
  7 purchase totals = $691.94       $731.1595   $731.17   $731.10   $731.20