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 $115.94   3.374%   $119.8518   $119.85   $119.85   $119.90  
  Purchase #2 $10.71   3.733%   $11.1098   $11.11   $11.10   $11.10  
  Purchase #3 $33.30   3.258%   $34.3849   $34.38   $34.40   $34.40  
  Purchase #4 $56.57   12.476%   $63.6277   $63.63   $63.65   $63.60  
  Purchase #5 $50.47   13.327%   $57.1961   $57.20   $57.20   $57.20  
  Purchase #6 $49.58   13.438%   $56.2426   $56.24   $56.25   $56.20  
  Purchase #7 $10.71   9.645%   $11.743   $11.74   $11.75   $11.70  
  7 purchase totals = $327.28       $354.1559   $354.15   $354.20   $354.10