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 $215.29   12.733%   $242.7029   $242.70   $242.70   $242.70  
  Purchase #2 $140.92   9.484%   $154.2849   $154.28   $154.30   $154.30  
  Purchase #3 $17.43   13.292%   $19.7468   $19.75   $19.75   $19.70  
  Purchase #4 $68.46   12.267%   $76.858   $76.86   $76.85   $76.90  
  Purchase #5 $151.35   3.500%   $156.6473   $156.65   $156.65   $156.60  
  Purchase #6 $22.47   5.701%   $23.751   $23.75   $23.75   $23.80  
  Purchase #7 $34.37   3.232%   $35.4808   $35.48   $35.50   $35.50  
  7 purchase totals = $650.29       $709.4717   $709.47   $709.50   $709.50