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 $23.62   12.649%   $26.6077   $26.61   $26.60   $26.60  
  Purchase #2 $87.40   6.231%   $92.8459   $92.85   $92.85   $92.80  
  Purchase #3 $13.25   5.139%   $13.9309   $13.93   $13.95   $13.90  
  Purchase #4 $231.30   9.282%   $252.7693   $252.77   $252.75   $252.80  
  Purchase #5 $212.50   6.201%   $225.6771   $225.68   $225.70   $225.70  
  Purchase #6 $66.89   7.551%   $71.9409   $71.94   $71.95   $71.90  
  Purchase #7 $60.86   7.583%   $65.475   $65.48   $65.50   $65.50  
  7 purchase totals = $695.82       $749.2468   $749.26   $749.30   $749.20