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 $104.65   6.223%   $111.1624   $111.16   $111.15   $111.20  
  Purchase #2 $55.40   3.393%   $57.2797   $57.28   $57.30   $57.30  
  Purchase #3 $124.72   7.487%   $134.0578   $134.06   $134.05   $134.10  
  Purchase #4 $10.92   5.298%   $11.4985   $11.50   $11.50   $11.50  
  Purchase #5 $130.30   4.774%   $136.5205   $136.52   $136.50   $136.50  
  Purchase #6 $244.92   6.159%   $260.0046   $260.00   $260.00   $260.00  
  Purchase #7 $87.97   9.866%   $96.6491   $96.65   $96.65   $96.60  
  7 purchase totals = $758.88       $807.1726   $807.17   $807.15   $807.20