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 $49.44   5.239%   $52.0302   $52.03   $52.05   $52.00  
  Purchase #2 $229.85   10.491%   $253.9636   $253.96   $253.95   $254.00  
  Purchase #3 $60.47   12.104%   $67.7893   $67.79   $67.80   $67.80  
  Purchase #4 $164.25   12.844%   $185.3463   $185.35   $185.35   $185.30  
  Purchase #5 $67.39   13.446%   $76.4513   $76.45   $76.45   $76.50  
  Purchase #6 $67.34   3.368%   $69.608   $69.61   $69.60   $69.60  
  Purchase #7 $80.51   4.326%   $83.9929   $83.99   $84.00   $84.00  
  7 purchase totals = $719.25       $789.1816   $789.18   $789.20   $789.20