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 $246.25   9.475%   $269.5822   $269.58   $269.60   $269.60  
  Purchase #2 $226.77   4.709%   $237.4486   $237.45   $237.45   $237.40  
  Purchase #3 $150.38   4.816%   $157.6223   $157.62   $157.60   $157.60  
  Purchase #4 $97.62   5.868%   $103.3483   $103.35   $103.35   $103.30  
  Purchase #5 $177.67   13.827%   $202.2364   $202.24   $202.25   $202.20  
  Purchase #6 $240.99   7.420%   $258.8715   $258.87   $258.85   $258.90  
  Purchase #7 $17.86   10.520%   $19.7389   $19.74   $19.75   $19.70  
  7 purchase totals = $1,157.54       $1,248.8482   $1,248.85   $1,248.85   $1,248.70