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 $206.99   3.306%   $213.8331   $213.83   $213.85   $213.80  
  Purchase #2 $110.90   3.779%   $115.0909   $115.09   $115.10   $115.10  
  Purchase #3 $245.98   5.862%   $260.3993   $260.40   $260.40   $260.40  
  Purchase #4 $121.42   4.411%   $126.7758   $126.78   $126.80   $126.80  
  Purchase #5 $84.43   13.476%   $95.8078   $95.81   $95.80   $95.80  
  Purchase #6 $160.66   3.607%   $166.455   $166.46   $166.45   $166.50  
  Purchase #7 $42.76   8.705%   $46.4823   $46.48   $46.50   $46.50  
  7 purchase totals = $973.14       $1,024.8442   $1,024.85   $1,024.90   $1,024.90