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 $89.97   6.709%   $96.0061   $96.01   $96.00   $96.00  
  Purchase #2 $245.36   6.772%   $261.9758   $261.98   $262.00   $262.00  
  Purchase #3 $214.95   4.546%   $224.7216   $224.72   $224.70   $224.70  
  Purchase #4 $60.55   11.259%   $67.3673   $67.37   $67.35   $67.40  
  Purchase #5 $128.47   6.833%   $137.2484   $137.25   $137.25   $137.20  
  Purchase #6 $192.51   4.246%   $200.684   $200.68   $200.70   $200.70  
  Purchase #7 $17.76   3.714%   $18.4196   $18.42   $18.40   $18.40  
  7 purchase totals = $949.57       $1,006.4228   $1,006.43   $1,006.40   $1,006.40