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 $230.54   13.328%   $261.2664   $261.27   $261.25   $261.30  
  Purchase #2 $175.36   9.589%   $192.1753   $192.18   $192.20   $192.20  
  Purchase #3 $186.91   11.127%   $207.7075   $207.71   $207.70   $207.70  
  Purchase #4 $169.99   6.822%   $181.5867   $181.59   $181.60   $181.60  
  Purchase #5 $213.99   8.453%   $232.0786   $232.08   $232.10   $232.10  
  Purchase #6 $63.65   13.188%   $72.0442   $72.04   $72.05   $72.00  
  Purchase #7 $101.35   6.403%   $107.8394   $107.84   $107.85   $107.80  
  7 purchase totals = $1,141.79       $1,254.6981   $1,254.71   $1,254.75   $1,254.70