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 $61.98   5.394%   $65.3232   $65.32   $65.30   $65.30  
  Purchase #2 $27.51   7.697%   $29.6274   $29.63   $29.65   $29.60  
  Purchase #3 $29.28   13.432%   $33.2129   $33.21   $33.20   $33.20  
  Purchase #4 $161.33   4.296%   $168.2607   $168.26   $168.25   $168.30  
  Purchase #5 $169.25   13.557%   $192.1952   $192.20   $192.20   $192.20  
  Purchase #6 $156.76   13.352%   $177.6906   $177.69   $177.70   $177.70  
  Purchase #7 $139.26   11.314%   $155.0159   $155.02   $155.00   $155.00  
  7 purchase totals = $745.37       $821.3259   $821.33   $821.30   $821.30