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 $240.81   12.657%   $271.2893   $271.29   $271.30   $271.30  
  Purchase #2 $224.25   13.653%   $254.8669   $254.87   $254.85   $254.90  
  Purchase #3 $175.44   10.545%   $193.9401   $193.94   $193.95   $193.90  
  Purchase #4 $188.59   7.410%   $202.5645   $202.56   $202.55   $202.60  
  Purchase #5 $90.85   5.632%   $95.9667   $95.97   $95.95   $96.00  
  Purchase #6 $241.41   10.149%   $265.9107   $265.91   $265.90   $265.90  
  Purchase #7 $156.76   8.135%   $169.5124   $169.51   $169.50   $169.50  
  7 purchase totals = $1,318.11       $1,454.0506   $1,454.05   $1,454.00   $1,454.10