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 $208.41   10.150%   $229.5636   $229.56   $229.55   $229.60  
  Purchase #2 $190.54   11.605%   $212.6522   $212.65   $212.65   $212.70  
  Purchase #3 $35.47   13.283%   $40.1815   $40.18   $40.20   $40.20  
  Purchase #4 $122.39   7.427%   $131.4799   $131.48   $131.50   $131.50  
  Purchase #5 $17.51   11.380%   $19.5026   $19.50   $19.50   $19.50  
  Purchase #6 $34.99   6.382%   $37.2231   $37.22   $37.20   $37.20  
  Purchase #7 $174.54   10.153%   $192.261   $192.26   $192.25   $192.30  
  7 purchase totals = $783.85       $862.8639   $862.85   $862.85   $863.00