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 $218.50   13.618%   $248.2553   $248.26   $248.25   $248.30  
  Purchase #2 $137.78   10.825%   $152.6947   $152.69   $152.70   $152.70  
  Purchase #3 $138.91   10.203%   $153.083   $153.08   $153.10   $153.10  
  Purchase #4 $237.61   10.465%   $262.4759   $262.48   $262.50   $262.50  
  Purchase #5 $219.79   12.563%   $247.4022   $247.40   $247.40   $247.40  
  Purchase #6 $45.85   13.176%   $51.8912   $51.89   $51.90   $51.90  
  Purchase #7 $164.69   5.294%   $173.4087   $173.41   $173.40   $173.40  
  7 purchase totals = $1,163.13       $1,289.2110   $1,289.21   $1,289.25   $1,289.30