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 $235.77   3.847%   $244.8401   $244.84   $244.85   $244.80  
  Purchase #2 $221.87   13.853%   $252.6057   $252.61   $252.60   $252.60  
  Purchase #3 $122.85   10.372%   $135.592   $135.59   $135.60   $135.60  
  Purchase #4 $129.46   3.553%   $134.0597   $134.06   $134.05   $134.10  
  Purchase #5 $215.96   9.663%   $236.8282   $236.83   $236.85   $236.80  
  Purchase #6 $56.78   5.538%   $59.9245   $59.92   $59.90   $59.90  
  Purchase #7 $184.88   3.664%   $191.654   $191.65   $191.65   $191.70  
  7 purchase totals = $1,167.57       $1,255.5042   $1,255.50   $1,255.50   $1,255.50