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 $24.74   12.213%   $27.7615   $27.76   $27.75   $27.80  
  Purchase #2 $106.80   5.115%   $112.2628   $112.26   $112.25   $112.30  
  Purchase #3 $76.42   13.557%   $86.7803   $86.78   $86.80   $86.80  
  Purchase #4 $147.62   4.572%   $154.3692   $154.37   $154.35   $154.40  
  Purchase #5 $214.55   6.799%   $229.1373   $229.14   $229.15   $229.10  
  Purchase #6 $43.92   12.559%   $49.4359   $49.44   $49.45   $49.40  
  Purchase #7 $208.77   3.216%   $215.484   $215.48   $215.50   $215.50  
  7 purchase totals = $822.82       $875.2310   $875.23   $875.25   $875.30