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 $213.35   12.780%   $240.6161   $240.62   $240.60   $240.60  
  Purchase #2 $51.42   10.396%   $56.7656   $56.77   $56.75   $56.80  
  Purchase #3 $49.44   13.237%   $55.9844   $55.98   $56.00   $56.00  
  Purchase #4 $82.35   8.290%   $89.1768   $89.18   $89.20   $89.20  
  Purchase #5 $214.99   13.610%   $244.2501   $244.25   $244.25   $244.30  
  Purchase #6 $58.48   5.552%   $61.7268   $61.73   $61.75   $61.70  
  Purchase #7 $103.67   5.556%   $109.4299   $109.43   $109.45   $109.40  
  7 purchase totals = $773.70       $857.9497   $857.96   $858.00   $858.00