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 $150.66   8.806%   $163.9271   $163.93   $163.95   $163.90  
  Purchase #2 $61.62   7.449%   $66.2101   $66.21   $66.20   $66.20  
  Purchase #3 $163.90   11.457%   $182.678   $182.68   $182.70   $182.70  
  Purchase #4 $29.99   13.839%   $34.1403   $34.14   $34.15   $34.10  
  Purchase #5 $247.58   6.316%   $263.2172   $263.22   $263.20   $263.20  
  Purchase #6 $168.26   6.639%   $179.4308   $179.43   $179.45   $179.40  
  Purchase #7 $22.38   9.665%   $24.543   $24.54   $24.55   $24.50  
  7 purchase totals = $844.39       $914.1465   $914.15   $914.20   $914.00