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 $11.39   8.427%   $12.3498   $12.35   $12.35   $12.30  
  Purchase #2 $115.32   7.603%   $124.0878   $124.09   $124.10   $124.10  
  Purchase #3 $143.41   12.367%   $161.1455   $161.15   $161.15   $161.10  
  Purchase #4 $63.93   3.188%   $65.9681   $65.97   $65.95   $66.00  
  Purchase #5 $120.58   3.120%   $124.3421   $124.34   $124.35   $124.30  
  Purchase #6 $201.99   4.503%   $211.0856   $211.09   $211.10   $211.10  
  Purchase #7 $24.51   4.542%   $25.6232   $25.62   $25.60   $25.60  
  7 purchase totals = $681.13       $724.6021   $724.61   $724.60   $724.50