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 $212.64   9.323%   $232.4644   $232.46   $232.45   $232.50  
  Purchase #2 $58.34   13.287%   $66.0916   $66.09   $66.10   $66.10  
  Purchase #3 $34.66   12.197%   $38.8875   $38.89   $38.90   $38.90  
  Purchase #4 $219.81   4.195%   $229.031   $229.03   $229.05   $229.00  
  Purchase #5 $179.99   5.855%   $190.5284   $190.53   $190.55   $190.50  
  Purchase #6 $163.76   10.188%   $180.4439   $180.44   $180.45   $180.40  
  Purchase #7 $192.67   9.468%   $210.912   $210.91   $210.90   $210.90  
  7 purchase totals = $1,061.87       $1,148.3588   $1,148.35   $1,148.40   $1,148.30