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 $219.52   13.847%   $249.9169   $249.92   $249.90   $249.90  
  Purchase #2 $72.41   6.161%   $76.8712   $76.87   $76.85   $76.90  
  Purchase #3 $47.91   3.302%   $49.492   $49.49   $49.50   $49.50  
  Purchase #4 $18.34   9.216%   $20.0302   $20.03   $20.05   $20.00  
  Purchase #5 $189.41   13.849%   $215.6414   $215.64   $215.65   $215.60  
  Purchase #6 $112.83   4.223%   $117.5948   $117.59   $117.60   $117.60  
  Purchase #7 $23.82   12.455%   $26.7868   $26.79   $26.80   $26.80  
  7 purchase totals = $684.24       $756.3333   $756.33   $756.35   $756.30