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 $208.46   13.827%   $237.2838   $237.28   $237.30   $237.30  
  Purchase #2 $226.89   11.215%   $252.3357   $252.34   $252.35   $252.30  
  Purchase #3 $62.73   3.713%   $65.0592   $65.06   $65.05   $65.10  
  Purchase #4 $242.34   13.299%   $274.5688   $274.57   $274.55   $274.60  
  Purchase #5 $33.81   3.160%   $34.8784   $34.88   $34.90   $34.90  
  Purchase #6 $230.32   10.772%   $255.1301   $255.13   $255.15   $255.10  
  Purchase #7 $104.45   11.570%   $116.5349   $116.53   $116.55   $116.50  
  7 purchase totals = $1,109.00       $1,235.7909   $1,235.79   $1,235.85   $1,235.80