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 $217.29   11.328%   $241.9046   $241.90   $241.90   $241.90  
  Purchase #2 $186.25   8.261%   $201.6361   $201.64   $201.65   $201.60  
  Purchase #3 $52.31   4.801%   $54.8214   $54.82   $54.80   $54.80  
  Purchase #4 $242.77   12.514%   $273.1502   $273.15   $273.15   $273.20  
  Purchase #5 $33.43   5.827%   $35.378   $35.38   $35.40   $35.40  
  Purchase #6 $173.72   3.802%   $180.3248   $180.32   $180.30   $180.30  
  Purchase #7 $60.87   10.468%   $67.2419   $67.24   $67.25   $67.20  
  7 purchase totals = $966.64       $1,054.4570   $1,054.45   $1,054.45   $1,054.40