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 $204.85   9.371%   $224.0465   $224.05   $224.05   $224.00  
  Purchase #2 $243.53   7.278%   $261.2541   $261.25   $261.25   $261.30  
  Purchase #3 $75.80   6.360%   $80.6209   $80.62   $80.60   $80.60  
  Purchase #4 $33.69   11.336%   $37.5091   $37.51   $37.50   $37.50  
  Purchase #5 $127.62   10.549%   $141.0826   $141.08   $141.10   $141.10  
  Purchase #6 $220.85   6.189%   $234.5184   $234.52   $234.50   $234.50  
  Purchase #7 $20.46   7.627%   $22.0205   $22.02   $22.00   $22.00  
  7 purchase totals = $926.80       $1,001.0521   $1,001.05   $1,001.00   $1,001.00