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 $208.35   3.734%   $216.1298   $216.13   $216.15   $216.10  
  Purchase #2 $38.96   12.552%   $43.8503   $43.85   $43.85   $43.90  
  Purchase #3 $226.84   6.105%   $240.6886   $240.69   $240.70   $240.70  
  Purchase #4 $18.44   10.235%   $20.3273   $20.33   $20.35   $20.30  
  Purchase #5 $224.77   12.549%   $252.9764   $252.98   $253.00   $253.00  
  Purchase #6 $40.95   12.373%   $46.0167   $46.02   $46.00   $46.00  
  Purchase #7 $190.98   6.252%   $202.9201   $202.92   $202.90   $202.90  
  7 purchase totals = $949.29       $1,022.9092   $1,022.92   $1,022.95   $1,022.90