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 $149.34   11.209%   $166.0795   $166.08   $166.10   $166.10  
  Purchase #2 $239.47   9.341%   $261.8389   $261.84   $261.85   $261.80  
  Purchase #3 $76.86   9.383%   $84.0718   $84.07   $84.05   $84.10  
  Purchase #4 $186.65   8.758%   $202.9968   $203.00   $203.00   $203.00  
  Purchase #5 $186.92   11.448%   $208.3186   $208.32   $208.30   $208.30  
  Purchase #6 $60.41   8.137%   $65.3256   $65.33   $65.35   $65.30  
  Purchase #7 $76.59   8.178%   $82.8535   $82.85   $82.85   $82.90  
  7 purchase totals = $976.24       $1,071.4847   $1,071.49   $1,071.50   $1,071.50