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 $91.59   4.373%   $95.5952   $95.60   $95.60   $95.60  
  Purchase #2 $236.38   10.659%   $261.5757   $261.58   $261.60   $261.60  
  Purchase #3 $10.31   13.842%   $11.7371   $11.74   $11.75   $11.70  
  Purchase #4 $49.85   10.572%   $55.1201   $55.12   $55.10   $55.10  
  Purchase #5 $214.37   12.373%   $240.894   $240.89   $240.90   $240.90  
  Purchase #6 $127.65   10.861%   $141.5141   $141.51   $141.50   $141.50  
  Purchase #7 $162.30   9.187%   $177.2105   $177.21   $177.20   $177.20  
  7 purchase totals = $892.45       $983.6467   $983.65   $983.65   $983.60