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 $27.61   7.243%   $29.6098   $29.61   $29.60   $29.60  
  Purchase #2 $213.90   12.647%   $240.9519   $240.95   $240.95   $241.00  
  Purchase #3 $139.76   9.613%   $153.1951   $153.20   $153.20   $153.20  
  Purchase #4 $49.30   6.597%   $52.5523   $52.55   $52.55   $52.60  
  Purchase #5 $182.57   5.157%   $191.9851   $191.99   $192.00   $192.00  
  Purchase #6 $90.31   13.716%   $102.6969   $102.70   $102.70   $102.70  
  Purchase #7 $155.60   10.555%   $172.0236   $172.02   $172.00   $172.00  
  7 purchase totals = $859.05       $943.0147   $943.02   $943.00   $943.10