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 $205.61   5.218%   $216.3387   $216.34   $216.35   $216.30  
  Purchase #2 $47.35   12.531%   $53.2834   $53.28   $53.30   $53.30  
  Purchase #3 $113.32   3.374%   $117.1434   $117.14   $117.15   $117.10  
  Purchase #4 $132.81   5.771%   $140.4745   $140.47   $140.45   $140.50  
  Purchase #5 $211.89   10.723%   $234.611   $234.61   $234.60   $234.60  
  Purchase #6 $77.32   3.483%   $80.0131   $80.01   $80.00   $80.00  
  Purchase #7 $209.78   13.271%   $237.6199   $237.62   $237.60   $237.60  
  7 purchase totals = $998.08       $1,079.4840   $1,079.47   $1,079.45   $1,079.40