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 $169.55   13.392%   $192.2561   $192.26   $192.25   $192.30  
  Purchase #2 $211.89   10.651%   $234.4584   $234.46   $234.45   $234.50  
  Purchase #3 $245.90   6.379%   $261.586   $261.59   $261.60   $261.60  
  Purchase #4 $52.53   5.716%   $55.5326   $55.53   $55.55   $55.50  
  Purchase #5 $232.61   9.285%   $254.2078   $254.21   $254.20   $254.20  
  Purchase #6 $154.30   4.163%   $160.7235   $160.72   $160.70   $160.70  
  Purchase #7 $109.26   5.525%   $115.2966   $115.30   $115.30   $115.30  
  7 purchase totals = $1,176.04       $1,274.0610   $1,274.07   $1,274.05   $1,274.10