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 $178.79   8.116%   $193.3006   $193.30   $193.30   $193.30  
  Purchase #2 $95.34   6.514%   $101.5504   $101.55   $101.55   $101.60  
  Purchase #3 $158.94   3.249%   $164.104   $164.10   $164.10   $164.10  
  Purchase #4 $93.72   8.463%   $101.6515   $101.65   $101.65   $101.70  
  Purchase #5 $174.82   8.811%   $190.2234   $190.22   $190.20   $190.20  
  Purchase #6 $149.31   13.651%   $169.6923   $169.69   $169.70   $169.70  
  Purchase #7 $45.99   3.349%   $47.5302   $47.53   $47.55   $47.50  
  7 purchase totals = $896.91       $968.0524   $968.04   $968.05   $968.10