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   6.561%   $69.0835   $69.08   $69.10   $69.10  
  Purchase #2 $227.88   13.182%   $257.9191   $257.92   $257.90   $257.90  
  Purchase #3 $129.58   8.724%   $140.8846   $140.88   $140.90   $140.90  
  Purchase #4 $76.59   13.227%   $86.7206   $86.72   $86.70   $86.70  
  Purchase #5 $161.58   9.314%   $176.6296   $176.63   $176.65   $176.60  
  Purchase #6 $147.93   7.377%   $158.8428   $158.84   $158.85   $158.80  
  Purchase #7 $66.66   11.433%   $74.2812   $74.28   $74.30   $74.30  
  7 purchase totals = $875.05       $964.3614   $964.35   $964.40   $964.30