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 $68.97   3.658%   $71.4929   $71.49   $71.50   $71.50  
  Purchase #2 $21.49   11.633%   $23.9899   $23.99   $24.00   $24.00  
  Purchase #3 $64.64   11.288%   $71.9366   $71.94   $71.95   $71.90  
  Purchase #4 $24.70   8.397%   $26.7741   $26.77   $26.75   $26.80  
  Purchase #5 $18.94   6.854%   $20.2381   $20.24   $20.25   $20.20  
  Purchase #6 $54.39   5.649%   $57.4625   $57.46   $57.45   $57.50  
  Purchase #7 $245.63   3.251%   $253.6154   $253.62   $253.60   $253.60  
  7 purchase totals = $498.76       $525.5095   $525.51   $525.50   $525.50