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 $74.70   3.104%   $77.0187   $77.02   $77.00   $77.00  
  Purchase #2 $173.98   5.166%   $182.9678   $182.97   $182.95   $183.00  
  Purchase #3 $60.27   10.259%   $66.4531   $66.45   $66.45   $66.50  
  Purchase #4 $109.51   9.531%   $119.9474   $119.95   $119.95   $119.90  
  Purchase #5 $222.84   8.174%   $241.0549   $241.05   $241.05   $241.10  
  Purchase #6 $32.46   11.659%   $36.2445   $36.24   $36.25   $36.20  
  Purchase #7 $68.38   4.549%   $71.4906   $71.49   $71.50   $71.50  
  7 purchase totals = $742.14       $795.1770   $795.17   $795.15   $795.20