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 $241.46   8.228%   $261.3273   $261.33   $261.35   $261.30  
  Purchase #2 $32.69   5.597%   $34.5197   $34.52   $34.50   $34.50  
  Purchase #3 $131.25   5.254%   $138.1459   $138.15   $138.15   $138.10  
  Purchase #4 $151.44   3.698%   $157.0403   $157.04   $157.05   $157.00  
  Purchase #5 $55.87   8.833%   $60.805   $60.81   $60.80   $60.80  
  Purchase #6 $233.29   10.145%   $256.9573   $256.96   $256.95   $257.00  
  Purchase #7 $241.88   7.514%   $260.0549   $260.05   $260.05   $260.10  
  7 purchase totals = $1,087.88       $1,168.8504   $1,168.86   $1,168.85   $1,168.80