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 $52.51   7.658%   $56.5312   $56.53   $56.55   $56.50  
  Purchase #2 $216.78   3.757%   $224.9244   $224.92   $224.90   $224.90  
  Purchase #3 $55.71   4.605%   $58.2754   $58.28   $58.30   $58.30  
  Purchase #4 $166.78   6.306%   $177.2971   $177.30   $177.30   $177.30  
  Purchase #5 $23.50   4.578%   $24.5758   $24.58   $24.60   $24.60  
  Purchase #6 $65.90   5.735%   $69.6794   $69.68   $69.70   $69.70  
  Purchase #7 $214.47   12.386%   $241.0343   $241.03   $241.05   $241.00  
  7 purchase totals = $795.65       $852.3176   $852.32   $852.40   $852.30