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 $233.39   12.661%   $262.9395   $262.94   $262.95   $262.90  
  Purchase #2 $149.95   5.637%   $158.4027   $158.40   $158.40   $158.40  
  Purchase #3 $105.81   6.868%   $113.077   $113.08   $113.10   $113.10  
  Purchase #4 $36.94   10.124%   $40.6798   $40.68   $40.70   $40.70  
  Purchase #5 $144.63   4.367%   $150.946   $150.95   $150.95   $150.90  
  Purchase #6 $74.70   5.374%   $78.7144   $78.71   $78.70   $78.70  
  Purchase #7 $194.37   6.263%   $206.5434   $206.54   $206.55   $206.50  
  7 purchase totals = $939.79       $1,011.3028   $1,011.30   $1,011.35   $1,011.20