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 $192.93   11.459%   $215.0378   $215.04   $215.05   $215.00  
  Purchase #2 $179.33   8.588%   $194.7309   $194.73   $194.75   $194.70  
  Purchase #3 $176.94   5.831%   $187.2574   $187.26   $187.25   $187.30  
  Purchase #4 $70.30   9.499%   $76.9778   $76.98   $77.00   $77.00  
  Purchase #5 $141.58   13.734%   $161.0246   $161.02   $161.00   $161.00  
  Purchase #6 $38.36   10.670%   $42.453   $42.45   $42.45   $42.50  
  Purchase #7 $115.62   6.866%   $123.5585   $123.56   $123.55   $123.60  
  7 purchase totals = $915.06       $1,001.0400   $1,001.04   $1,001.05   $1,001.10