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 $231.62   13.370%   $262.5876   $262.59   $262.60   $262.60  
  Purchase #2 $5.69   10.436%   $6.2838   $6.28   $6.30   $6.30  
  Purchase #3 $74.42   9.177%   $81.2495   $81.25   $81.25   $81.20  
  Purchase #4 $151.85   4.751%   $159.0644   $159.06   $159.05   $159.10  
  Purchase #5 $168.87   12.674%   $190.2726   $190.27   $190.25   $190.30  
  Purchase #6 $79.33   11.542%   $88.4863   $88.49   $88.50   $88.50  
  Purchase #7 $242.51   4.332%   $253.0155   $253.02   $253.00   $253.00  
  7 purchase totals = $954.29       $1,040.9597   $1,040.96   $1,040.95   $1,041.00