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 $172.30   4.500%   $180.0535   $180.05   $180.05   $180.10  
  Purchase #2 $61.58   5.798%   $65.1504   $65.15   $65.15   $65.20  
  Purchase #3 $129.54   10.581%   $143.2466   $143.25   $143.25   $143.20  
  Purchase #4 $71.66   13.230%   $81.1406   $81.14   $81.15   $81.10  
  Purchase #5 $35.91   8.657%   $39.0187   $39.02   $39.00   $39.00  
  Purchase #6 $45.41   8.417%   $49.2322   $49.23   $49.25   $49.20  
  Purchase #7 $113.35   9.566%   $124.1931   $124.19   $124.20   $124.20  
  7 purchase totals = $629.75       $682.0351   $682.03   $682.05   $682.00