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 $95.80   8.851%   $104.2793   $104.28   $104.30   $104.30  
  Purchase #2 $225.80   12.418%   $253.8398   $253.84   $253.85   $253.80  
  Purchase #3 $54.61   9.522%   $59.81   $59.81   $59.80   $59.80  
  Purchase #4 $238.91   9.287%   $261.0976   $261.10   $261.10   $261.10  
  Purchase #5 $176.87   5.509%   $186.6138   $186.61   $186.60   $186.60  
  Purchase #6 $154.85   7.250%   $166.0766   $166.08   $166.10   $166.10  
  Purchase #7 $234.27   8.643%   $254.518   $254.52   $254.50   $254.50  
  7 purchase totals = $1,181.11       $1,286.2351   $1,286.24   $1,286.25   $1,286.20