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 $208.37   8.470%   $226.0189   $226.02   $226.00   $226.00  
  Purchase #2 $119.46   11.839%   $133.6029   $133.60   $133.60   $133.60  
  Purchase #3 $76.78   4.478%   $80.2182   $80.22   $80.20   $80.20  
  Purchase #4 $158.58   11.579%   $176.942   $176.94   $176.95   $176.90  
  Purchase #5 $187.78   5.228%   $197.5971   $197.60   $197.60   $197.60  
  Purchase #6 $98.75   13.517%   $112.098   $112.10   $112.10   $112.10  
  Purchase #7 $127.83   13.307%   $144.8403   $144.84   $144.85   $144.80  
  7 purchase totals = $977.55       $1,071.3174   $1,071.32   $1,071.30   $1,071.20