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 $101.86   13.158%   $115.2627   $115.26   $115.25   $115.30  
  Purchase #2 $153.72   7.278%   $164.9077   $164.91   $164.90   $164.90  
  Purchase #3 $71.63   3.698%   $74.2789   $74.28   $74.30   $74.30  
  Purchase #4 $48.93   3.765%   $50.7722   $50.77   $50.75   $50.80  
  Purchase #5 $223.92   9.147%   $244.402   $244.40   $244.40   $244.40  
  Purchase #6 $70.30   11.429%   $78.3346   $78.33   $78.35   $78.30  
  Purchase #7 $150.43   10.145%   $165.6911   $165.69   $165.70   $165.70  
  7 purchase totals = $820.79       $893.6492   $893.64   $893.65   $893.70