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 $34.62   11.145%   $38.4784   $38.48   $38.50   $38.50  
  Purchase #2 $248.90   5.113%   $261.6263   $261.63   $261.65   $261.60  
  Purchase #3 $103.85   11.268%   $115.5518   $115.55   $115.55   $115.60  
  Purchase #4 $190.45   10.836%   $211.0872   $211.09   $211.10   $211.10  
  Purchase #5 $65.78   8.372%   $71.2871   $71.29   $71.30   $71.30  
  Purchase #6 $110.50   7.671%   $118.9765   $118.98   $119.00   $119.00  
  Purchase #7 $177.71   5.598%   $187.6582   $187.66   $187.65   $187.70  
  7 purchase totals = $931.81       $1,004.6655   $1,004.68   $1,004.75   $1,004.80