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 $56.95   7.256%   $61.0823   $61.08   $61.10   $61.10  
  Purchase #2 $243.40   9.225%   $265.8537   $265.85   $265.85   $265.90  
  Purchase #3 $28.97   5.149%   $30.4617   $30.46   $30.45   $30.50  
  Purchase #4 $230.64   4.288%   $240.5298   $240.53   $240.55   $240.50  
  Purchase #5 $119.33   12.581%   $134.3429   $134.34   $134.35   $134.30  
  Purchase #6 $68.95   12.692%   $77.7011   $77.70   $77.70   $77.70  
  Purchase #7 $5.53   3.138%   $5.7035   $5.70   $5.70   $5.70  
  7 purchase totals = $753.77       $815.6750   $815.66   $815.70   $815.70