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 $22.42   8.260%   $24.2719   $24.27   $24.25   $24.30  
  Purchase #2 $73.83   10.219%   $81.3747   $81.37   $81.35   $81.40  
  Purchase #3 $250.88   8.809%   $272.98   $272.98   $273.00   $273.00  
  Purchase #4 $163.54   8.523%   $177.4785   $177.48   $177.50   $177.50  
  Purchase #5 $120.53   4.438%   $125.8791   $125.88   $125.90   $125.90  
  Purchase #6 $196.33   8.737%   $213.4834   $213.48   $213.50   $213.50  
  Purchase #7 $128.75   13.308%   $145.8841   $145.88   $145.90   $145.90  
  7 purchase totals = $956.28       $1,041.3517   $1,041.34   $1,041.40   $1,041.50