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 $39.35   11.305%   $43.7985   $43.80   $43.80   $43.80  
  Purchase #2 $223.45   5.677%   $236.1353   $236.14   $236.15   $236.10  
  Purchase #3 $53.63   6.169%   $56.9384   $56.94   $56.95   $56.90  
  Purchase #4 $150.51   3.811%   $156.2459   $156.25   $156.25   $156.20  
  Purchase #5 $25.39   5.201%   $26.7105   $26.71   $26.70   $26.70  
  Purchase #6 $228.66   10.641%   $252.9917   $252.99   $253.00   $253.00  
  Purchase #7 $232.78   6.215%   $247.2473   $247.25   $247.25   $247.20  
  7 purchase totals = $953.77       $1,020.0676   $1,020.08   $1,020.10   $1,019.90