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 $104.60   13.857%   $119.0944   $119.09   $119.10   $119.10  
  Purchase #2 $232.68   12.199%   $261.0646   $261.06   $261.05   $261.10  
  Purchase #3 $90.35   11.398%   $100.6481   $100.65   $100.65   $100.60  
  Purchase #4 $87.84   11.578%   $98.0101   $98.01   $98.00   $98.00  
  Purchase #5 $169.56   5.153%   $178.2974   $178.30   $178.30   $178.30  
  Purchase #6 $13.44   10.424%   $14.841   $14.84   $14.85   $14.80  
  Purchase #7 $147.81   10.423%   $163.2162   $163.22   $163.20   $163.20  
  7 purchase totals = $846.28       $935.1718   $935.17   $935.15   $935.10