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 $162.64   10.460%   $179.6521   $179.65   $179.65   $179.70  
  Purchase #2 $154.54   8.643%   $167.8969   $167.90   $167.90   $167.90  
  Purchase #3 $15.94   10.200%   $17.5659   $17.57   $17.55   $17.60  
  Purchase #4 $91.71   7.542%   $98.6268   $98.63   $98.65   $98.60  
  Purchase #5 $137.70   9.105%   $150.2376   $150.24   $150.25   $150.20  
  Purchase #6 $179.75   11.506%   $200.432   $200.43   $200.45   $200.40  
  Purchase #7 $97.35   7.531%   $104.6814   $104.68   $104.70   $104.70  
  7 purchase totals = $839.63       $919.0927   $919.10   $919.15   $919.10