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 $228.87   8.829%   $249.0769   $249.08   $249.10   $249.10  
  Purchase #2 $97.82   12.131%   $109.6865   $109.69   $109.70   $109.70  
  Purchase #3 $42.96   12.385%   $48.2806   $48.28   $48.30   $48.30  
  Purchase #4 $28.64   5.797%   $30.3003   $30.30   $30.30   $30.30  
  Purchase #5 $221.41   6.213%   $235.1662   $235.17   $235.15   $235.20  
  Purchase #6 $56.83   8.736%   $61.7947   $61.79   $61.80   $61.80  
  Purchase #7 $56.44   6.813%   $60.2853   $60.29   $60.30   $60.30  
  7 purchase totals = $732.97       $794.5905   $794.60   $794.65   $794.70