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 $186.61   11.871%   $208.7625   $208.76   $208.75   $208.80  
  Purchase #2 $49.79   9.822%   $54.6804   $54.68   $54.70   $54.70  
  Purchase #3 $70.71   7.404%   $75.9454   $75.95   $75.95   $75.90  
  Purchase #4 $205.93   3.549%   $213.2385   $213.24   $213.25   $213.20  
  Purchase #5 $71.28   10.276%   $78.6047   $78.60   $78.60   $78.60  
  Purchase #6 $242.45   4.804%   $254.0973   $254.10   $254.10   $254.10  
  Purchase #7 $188.49   3.553%   $195.187   $195.19   $195.20   $195.20  
  7 purchase totals = $1,015.26       $1,080.5158   $1,080.52   $1,080.55   $1,080.50