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 $239.83   11.291%   $266.9092   $266.91   $266.90   $266.90  
  Purchase #2 $197.51   3.126%   $203.6842   $203.68   $203.70   $203.70  
  Purchase #3 $69.69   6.313%   $74.0895   $74.09   $74.10   $74.10  
  Purchase #4 $247.95   13.394%   $281.1604   $281.16   $281.15   $281.20  
  Purchase #5 $40.57   6.663%   $43.2732   $43.27   $43.25   $43.30  
  Purchase #6 $77.92   4.807%   $81.6656   $81.67   $81.65   $81.70  
  Purchase #7 $172.75   5.299%   $181.904   $181.90   $181.90   $181.90  
  7 purchase totals = $1,046.22       $1,132.6861   $1,132.68   $1,132.65   $1,132.80