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 $65.95   5.337%   $69.4698   $69.47   $69.45   $69.50  
  Purchase #2 $107.73   10.807%   $119.3724   $119.37   $119.35   $119.40  
  Purchase #3 $48.44   4.410%   $50.5762   $50.58   $50.60   $50.60  
  Purchase #4 $59.98   7.666%   $64.5781   $64.58   $64.60   $64.60  
  Purchase #5 $176.77   5.370%   $186.2625   $186.26   $186.25   $186.30  
  Purchase #6 $177.25   8.823%   $192.8888   $192.89   $192.90   $192.90  
  Purchase #7 $154.34   12.271%   $173.2791   $173.28   $173.30   $173.30  
  7 purchase totals = $790.46       $856.4269   $856.43   $856.45   $856.60