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 $50.31   11.748%   $56.2204   $56.22   $56.20   $56.20  
  Purchase #2 $109.86   8.377%   $119.063   $119.06   $119.05   $119.10  
  Purchase #3 $208.56   4.487%   $217.9181   $217.92   $217.90   $217.90  
  Purchase #4 $39.44   11.335%   $43.9105   $43.91   $43.90   $43.90  
  Purchase #5 $206.80   8.736%   $224.866   $224.87   $224.85   $224.90  
  Purchase #6 $140.67   13.734%   $159.9896   $159.99   $160.00   $160.00  
  Purchase #7 $184.65   8.663%   $200.6462   $200.65   $200.65   $200.60  
  7 purchase totals = $940.29       $1,022.6138   $1,022.62   $1,022.55   $1,022.60