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 $188.28   10.660%   $208.3506   $208.35   $208.35   $208.40  
  Purchase #2 $86.59   11.207%   $96.2941   $96.29   $96.30   $96.30  
  Purchase #3 $95.55   12.837%   $107.8158   $107.82   $107.80   $107.80  
  Purchase #4 $65.71   13.631%   $74.6669   $74.67   $74.65   $74.70  
  Purchase #5 $48.94   12.447%   $55.0316   $55.03   $55.05   $55.00  
  Purchase #6 $57.58   11.332%   $64.105   $64.11   $64.10   $64.10  
  Purchase #7 $151.51   11.783%   $169.3624   $169.36   $169.35   $169.40  
  7 purchase totals = $694.16       $775.6264   $775.63   $775.60   $775.70