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 $240.52   8.503%   $260.9714   $260.97   $260.95   $261.00  
  Purchase #2 $139.28   12.348%   $156.4783   $156.48   $156.50   $156.50  
  Purchase #3 $106.81   11.718%   $119.326   $119.33   $119.35   $119.30  
  Purchase #4 $214.27   6.861%   $228.9711   $228.97   $228.95   $229.00  
  Purchase #5 $52.27   3.379%   $54.0362   $54.04   $54.05   $54.00  
  Purchase #6 $183.41   12.156%   $205.7053   $205.71   $205.70   $205.70  
  Purchase #7 $157.66   10.611%   $174.3893   $174.39   $174.40   $174.40  
  7 purchase totals = $1,094.22       $1,199.8776   $1,199.89   $1,199.90   $1,199.90