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 $64.83   12.850%   $73.1607   $73.16   $73.15   $73.20  
  Purchase #2 $99.25   8.759%   $107.9433   $107.94   $107.95   $107.90  
  Purchase #3 $76.60   12.595%   $86.2478   $86.25   $86.25   $86.20  
  Purchase #4 $190.67   4.346%   $198.9565   $198.96   $198.95   $199.00  
  Purchase #5 $153.40   12.520%   $172.6057   $172.61   $172.60   $172.60  
  Purchase #6 $98.70   10.418%   $108.9826   $108.98   $109.00   $109.00  
  Purchase #7 $110.58   5.314%   $116.4562   $116.46   $116.45   $116.50  
  7 purchase totals = $794.03       $864.3528   $864.36   $864.35   $864.40