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 $54.65   4.784%   $57.2645   $57.26   $57.25   $57.30  
  Purchase #2 $43.67   6.379%   $46.4557   $46.46   $46.45   $46.50  
  Purchase #3 $233.33   8.683%   $253.59   $253.59   $253.60   $253.60  
  Purchase #4 $67.93   5.268%   $71.5086   $71.51   $71.50   $71.50  
  Purchase #5 $204.87   4.581%   $214.2551   $214.26   $214.25   $214.30  
  Purchase #6 $202.48   5.815%   $214.2542   $214.25   $214.25   $214.30  
  Purchase #7 $90.61   6.358%   $96.371   $96.37   $96.35   $96.40  
  7 purchase totals = $897.54       $953.6991   $953.70   $953.65   $953.90