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 $82.77   5.390%   $87.2313   $87.23   $87.25   $87.20  
  Purchase #2 $221.64   6.595%   $236.2572   $236.26   $236.25   $236.30  
  Purchase #3 $60.34   5.429%   $63.6159   $63.62   $63.60   $63.60  
  Purchase #4 $250.90   5.693%   $265.1837   $265.18   $265.20   $265.20  
  Purchase #5 $98.62   7.243%   $105.763   $105.76   $105.75   $105.80  
  Purchase #6 $43.45   3.206%   $44.843   $44.84   $44.85   $44.80  
  Purchase #7 $183.38   10.551%   $202.7284   $202.73   $202.75   $202.70  
  7 purchase totals = $941.10       $1,005.6225   $1,005.62   $1,005.65   $1,005.60