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 $69.85   11.707%   $78.0273   $78.03   $78.05   $78.00  
  Purchase #2 $208.78   13.107%   $236.1448   $236.14   $236.15   $236.10  
  Purchase #3 $54.48   6.174%   $57.8436   $57.84   $57.85   $57.80  
  Purchase #4 $194.66   6.849%   $207.9923   $207.99   $208.00   $208.00  
  Purchase #5 $244.81   13.526%   $277.923   $277.92   $277.90   $277.90  
  Purchase #6 $197.61   4.128%   $205.7673   $205.77   $205.75   $205.80  
  Purchase #7 $41.44   9.821%   $45.5098   $45.51   $45.50   $45.50  
  7 purchase totals = $1,011.63       $1,109.2081   $1,109.20   $1,109.20   $1,109.10