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 $9.56   13.611%   $10.8612   $10.86   $10.85   $10.90  
  Purchase #2 $98.96   9.148%   $108.0129   $108.01   $108.00   $108.00  
  Purchase #3 $9.73   3.688%   $10.0888   $10.09   $10.10   $10.10  
  Purchase #4 $207.69   13.572%   $235.8777   $235.88   $235.90   $235.90  
  Purchase #5 $148.38   13.405%   $168.2703   $168.27   $168.25   $168.30  
  Purchase #6 $48.44   5.472%   $51.0906   $51.09   $51.10   $51.10  
  Purchase #7 $123.74   7.595%   $133.1381   $133.14   $133.15   $133.10  
  7 purchase totals = $646.50       $717.3396   $717.34   $717.35   $717.40