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 $222.70   13.625%   $253.0429   $253.04   $253.05   $253.00  
  Purchase #2 $219.84   3.698%   $227.9697   $227.97   $227.95   $228.00  
  Purchase #3 $89.64   8.116%   $96.9152   $96.92   $96.90   $96.90  
  Purchase #4 $62.41   10.807%   $69.1546   $69.15   $69.15   $69.20  
  Purchase #5 $250.35   9.619%   $274.4312   $274.43   $274.45   $274.40  
  Purchase #6 $8.66   4.538%   $9.053   $9.05   $9.05   $9.10  
  Purchase #7 $207.36   12.128%   $232.5086   $232.51   $232.50   $232.50  
  7 purchase totals = $1,060.96       $1,163.0752   $1,163.07   $1,163.05   $1,163.10